Elizabeth Carnegie
email: elizabeth.carnegie@northumbria.ac.uk

Jerzy Kociatkiewicz

Keywords: heritage management, monuments, politics, qualitative research, reflexivity, sustainable tourism

published or not. The documents may come

Introduction [START_REF] Bauman | Liquid Modernity[END_REF] famously described our current condition as that of liquid modernity: times of rapid change and unstable social structures. In times of such flux, individual actors tend to enjoy longer lifespans than the institutions governing their lives [START_REF] Bauman | Identity: Conversations with Benedetto Vecchi[END_REF]. While this has not stopped the practice of glorifying public triumphs (or aspirations) and the political status quo through the erection of imposing statues and monumental buildings, it does imply that such landmarks are likely to, relatively quickly, witness dramatic revalorisation(s) of their status and significance. However, their very solidity and apparent importance mean that such revalorisation is symbolically charged and can lead to a problematic and disputed afterlife. Wells (2007: 139) notes that because the purpose of monuments is often to commemorate a particular moment in a government's ascendancy and at the same time to insist on the permanence or atemporality of its rule, they are, of course, difficult to dispose of.

Our article is an attempt to take stock of the variety of fates of disgraced monuments and to investigate their possible roles in forming a basis for sustainable tourism and peace-oriented heritage (Wallis, 2019). We contend that tourists explore these sites under consideration here at the point where past and present meet and merge with their own expectations of place.

Our main insights come from a study of recent history museum and memory sites in Central and Eastern Europe, particularly those including (or consisting of) collections of communist-era monuments. Consequently, our focus concerns the fate of communist monuments in post-communist Central and Eastern Europe, but we believe the relevance of our analysis stretches much further, and thus we highlight some of the parallels to events and reconfigurations touching on other ideologies and political shifts. Taken as a paradigm case [START_REF] Flyvbjerg | Five misunderstandings about case-study research[END_REF] for the wider processes of reconsidering meaning of past monuments, our research sites offer a "mature" case study which benefits from a long-term view on the ways in which monuments and statues of former political leaders are treated before, during and, particularly, after a significant sociopolitical shift. The main conundrum at the heart of this article is the juxtaposition of the solidity and apparent immutability of statues and their changing interpretations, as reflected in shifts in their treatment and in varying reception over time, and at different sites, by their local and international viewers. Consequently, our key aim in this article is to work towards an understanding of the complex ways that nations, communities and localities deal with these once powerful and now symbolic tangible remnants of the recent past in order to shape and, indeed, consolidate the political present.

The contribution of our study lies in providing a field study-derived structuring for the reflection on the afterlife of monumental statues. The study follows a story starting with collapse of the political and rhetorical regime supporting monuments in their original context [START_REF] Dresser | Set in stone? Statues and slavery in London[END_REF][START_REF] Poria | Attitudes and willingness to donate towards heritage restoration: an exploratory study about Bulgarian socialist monuments[END_REF]. We explore how the various approaches to destruction, banishment and subsequent redisplays and re-contextualisation of the material icons of the recent political past are used in attempts to build and support peace, stability and sustainability over the period of thirty years following seismic political change throughout the region. We examine how these tangible, often monumental, objects become subject to being physically moved, damaged or destroyed [START_REF] Goodrich | What are statues good for? Winning the battle or losing the battleground?[END_REF][START_REF] Hautamäki | Heritage of the Finnish Civil War monuments in Tampere[END_REF]. The complexity lies in the myriad of ways that individual and collective local, national and tourist remembering differs, colludes and collides with the formal narratives of contemporary place-making. We determine that the various approaches to these problematic and tangible remnants work towards the goal of maintaining and ideally ensuring political and historical sustainability of the present within the liquid modern world of rapidly changing contexts.

Construction of place-based memory in the political present Crane (2000:2) defines memory as the "act of thinking about things in their absence" and notes that memories can be triggered consciously by the desire to remember and subconsciously and even unwelcome where there is the desire to forget. Museums and heritage sites function as containers of memory [START_REF] Assmann | Collective memory and cultural identity[END_REF][START_REF] Carnegie | It wasn't all bad': Representations of working class cultures within social history museums and their impacts on audiences[END_REF][START_REF] Carnegie | Curating people? Museum mediated memories and the politics of representation[END_REF] and may be shaped to promote national or local narratives of social and collective remembering, yet as individual memories are unique to that individual, so too will be their responses to such objects and displays [START_REF] Bennett | Stored virtue: Memory, the body and the evolutionary museum[END_REF]. Constructed visions and versions of the past may fit the need of the political present, but can clash with memories triggered by the places and objects encountered through museum and heritage visits. We argue that changing the context under which objects (here monumental statuary) are viewed and thus understood gives them new meaning in the present but does not necessarily succeed in destroying or changing the range of personal memories and associations that deny national narratives [START_REF] Tunbridge | Difficult Histories and Positive Identities[END_REF]. [START_REF] Drozdzewski | The significance of memory in the present[END_REF] follow Hill (2013: 381) in asserting that memory is enmeshed in everyday corporality through "practices of incorporation" and "practices of inscription," and argue that memory is articulated, felt, enacted, and experienced through the body, and the body is thus a place of memory. Violence facilitates the construction of "remembrance-scapes" that also serve to locate memory's absent presence, and people who have suffered loss or trauma or political change often return to geographical locations associated with these events; the sites remain central to how individuals and nations maintain memories. Memories of place are both spatially constituted in concrete or physical form, and constructed through narrative and memories of events. Consequently, places in memory can function as positioning tools for building, anchoring, and maintaining identities. As Zhang et al. (2018: 116) note, "heritage production, (re) presentation and consumption are closely connected to place promotion power relations, whilst identity (re)construction is often seen as a negotiation between dynamic and contested heritage discourses".

Despite the existence of real sites of memory and mourning associated with events, governments often chose to "place memory" by constructing sites of mourning such as war memorials in strategic locales within cities [START_REF] Drozdzewski | The significance of memory in the present[END_REF]. Formal remembering is encouraged as the new sites become the symbolic spaces of memory even when they do not have an actual relationship to war, atrocity or political change that is being remembered or, in the case of this article, consciously disremembered. Pivotal to memory's power is its politics and social usefulness [START_REF] Bell | The ghosts of place[END_REF], stressing its importance in embodying and sustaining value systems and stability.

Here, we examine the opposite process, showing how destruction or banishment of the objects of memory constitutes an attempt to eradicate the memories themselves, or at least to change the context for remembering. The aim is not easily achieved: objects continue to maintain ghostly presence at original sites in the memories of people interviewed for our study. As [START_REF] Beardslee | Whom does heritage empower, and whom does it silence? Intangible cultural heritage at the Jemaa el Fnaa, Marrakech[END_REF] points out, intangible heritage does not necessarily require physical contact with sites of commemoration.

Our interest began with the movement of bodies through heritage sites, and the movement of memories: embodied, carried, and emerging as narratives which complement, define or challenge the contemporary readings of space. Statues, the focus of our particular attention, are non-human actors who mimic bodies and their movement, whether in celebration, or, as is the case in the studied sites, in the violence of banishment, mockery, or destruction. Their destruction or displacement is a political act rife with meaning and only the seeming opposite of the erection of new memorial spaces for collective remembering and mourning.

Yet the significance of such actions reaches beyond the grand political gesture. The incorporeal bodies, the "unsettling" representations of "ghosts of place" are removed from symbolic and important spaces where they have been landmarks in the daily lives of people beyond their political associations to spaces where they do not belong. These symbols of a shared national and indeed local history are not erased by the symbolic destruction of their likenesses; they acquire new meaning, possibly supporting the political present yet still provide powerful, possibly painful and even whimsical links to the past.

Even when partially destroyed, as Feldman (2006: 261) argues in relation to memories of the Holocaust, object fragments still retain power to "conjure images of the social body and in their ability to reanimate the social body". This paradox of power and powerlessness is also evident in the monumental statues of the deposed, dangerous as symbols of a political past and yet more readily destructible than the memories of associated deeds and impact on the community. The destruction of images, the rendering them down to size as splintered broken bodies and the banishment of "whole bodies" out of context or within a carefully curated setting to walled and heritagized spaces, changes their meaning in the present but not their past. [START_REF] Feldman | Contact points: Museums and the lost body problem[END_REF] discusses the missing body problem and the impossibility of embodying experience in traditional museum settings. Yet as tourists bring their bodies, as local visitors bring their memories, they people these displays and reanimate them, in agreement or tension with the ways intended by the organisers and funders.

Monuments as constructed spaces Williams (2007: 5) describes how the establishment of monuments to WWI events created "social practices of visitations", and how continued visits and touristic appreciation rendered them sites "of cultural significance". He sees visitations to sites of memory and mourning as part of the long tradition of pilgrimage and funerary rites, and argues that they necessitate some form of reflection on what the visitor has learned: a physical as well as cognitive engagement linked to place. Edson (2017: 21) claims that people are "better informed today about world events in part due to technology" and are more sophisticated and demanding. The mostly international visitors to statue parks are both knowledgeable and largely interested in learning more through the actual engagement with symbolic spaces, albeit those constructed as a consequence of the act of banishment and revisionism.

For Milton (2011: 163), violent acts on sites and monuments cannot simply be termed violence of iconoclasm: such acts are a way of aggressive rewriting of a narrative of the past that contrasts with or challenges the objects' or sites' meaning in the present. Herscher (2011: 151) discusses how states, "post-conflict or otherwise", seek to preserve places, mobilising heritage to serve their own aims, as in the case of statues mobilised to populate new heritagized spaces away from their previous, often symbolic and outwardly political, contexts. Many forms of remembering and forgetting as present concurrently and, we contend, elicit varied emotional responses from tourists and locals alike. However, political sustainability requires the formal narratives to dominate through and despite the myriad of competing "voices" and memories [START_REF] Tunbridge | Difficult Histories and Positive Identities[END_REF][START_REF] Ashworth | Heritage, identity and Europe[END_REF]. Key questions remain: what purpose do these spaces serve in sustaining "appropriate" or politically useful visions and versions of regimes? Can they freeze the memories in the way the statues are frozen, suspended in artificial groupings and forced into a single representation of their role and significance in complex pasts? Who might these museums be for, as opposed to why they were created in the early spirit of change? We attempt to tackle these questions by examining who the actual local and tourist visitors are and how they remember or fit the depicted past within their own frames of reference and expectations of place. In short, we seek to determine how memories or viewpoints are sustained or changed by the encounter, and to question how visitors, in particular international visitors support the use of such spaces to reinforce messages of peace in the political present [START_REF] Light | Facing the future': tourism and identity building in post-socialist Romania[END_REF][START_REF] Higgins-Desbiolles | Challenging peace through tourism[END_REF][START_REF] Farmaki | The tourism and peace nexus[END_REF].

We are concerned with timelines and with temporal and relational distance to past events affecting the responses to and treatment of symbolic figureheads and political monuments of the past. Time alone does not fix narratives or ensure that they fade from memory in linear ways [START_REF] Healy | Social memory and historical justice: Introduction[END_REF]. Indeed, in an era lacking stable structures, extant narratives and representations continually risk becoming uninteresting, unhelpful, or subversive when viewed against emerging consensuses and newly dominant values [START_REF] Ashworth | Heritage, identity and Europe[END_REF][START_REF] Rivera | Managing "spoiled" national identity: War, tourism, and memory in Croatia[END_REF]. Recent contestations of colonialism, structural racism, and heteronormativity underscore precariousness of triumphal celebrations of past successes [START_REF] Goodrich | What are statues good for? Winning the battle or losing the battleground?[END_REF].

While formal narratives strive to solidify political stability in the present, memories ebb and flow and are subject to revisionism, generational shift and can be triggered by political unrest or citizen dissatisfaction. Our study suggests that heritagization of political pasts positively engages both the local population and the largely foreign visitors, and thus supports sustainable political strategies. These, in turn, are influenced by the expectations of tourist audiences wittingly or unwittingly supporting visited representations, with heritagized spaces shaped for tourist audiences or at least owing their continued existence to outside interest [START_REF] Capitello | Exploring place image from visitors' expected and lived experiences: A discrete choice approach[END_REF].

Methodology

The fieldwork material of our study consists of ethnographic observations and interviews with visitors and curatorial staff carried out in museums and memorial sites in Estonia, Germany, Hungary, Latvia, Lithuania, Russia, and Poland between 2016 and 2019, as part of a project investigating relationships between visitors and recent history exhibitions in Central and Eastern Europe. In line with most common ethnographic practice (Clifford and Marcus, 1986;[START_REF] Goodall | Writing the New Ethnography[END_REF], our fieldwork was oriented towards understanding the field rather than towards finding answers to any pre-specified research question. Consequently, only small amounts of the material we collected turn out to be relevant to the topic of the article: the afterlife of statues representing the communist past. For this reason, in the following discussion we draw primarily on our research at three sites focused specifically on preservation and exhibition of political art of the past regimes: Memento Park near Budapest in Hungary, Grūtas Park near Druskininkai in Lithuania, and a statue park at the Museum of National History in Tallinn, Estonia. Our collected material consists of field notes, interviews, and discussion notes. We agree with Erll (2011: 110) that "memories are robustly plural" and with Ashworth (2008) and [START_REF] Tucker | World heritage and the contradictions of 'universal value[END_REF] who stress the impossibility of plurality within dominant narratives in the political present. Thus, our summary is an abstraction of the multiple and multifaceted ways in which tourists construct and shape their own knowledge and experience of the contexts being remembered. Indeed, these experiences are often reflected on in the months and years after the visits, helping to fix or at least disseminate contemporary and shaped readings of the past.

While the study is not autoethnographic, our observations are necessarily influenced by our own backgrounds and viewpoints. In particular, we draw on our conflicting and complementary stances: while we are both academics working in Western Europe, one of us brings discipline knowledge of heritage and museum studies, and the other the personal experience of growing up and continued political engagement in the region coupled with a sociological perspective. Consequently, our observations include our own responses as insider/outsider, academics and tourists, observers and witnesses to cultural change.

However, as the aim of this article is to present a generalizing argument rather than a report on the field, we present our findings in a more summarizing vein than is usual in ethnographic and ethnographyinspired studies. With concision in mind, we have restrained from presenting the sties through direct quotations from interviews and field notes, integrating the description with our discussion of the concepts we find important.

The field study

In the sections, we present concise descriptions of three sites important to our argument: Memento Park in Hungary, Grūtas Park in Lithuania, and the statue park of the Estonian History Museum. Each consists of a grouping of monumental statues, but the exposition, arrangement, and information provided differs widely. We present them not just as research sites, but as exemplars of different ways of presenting the monumental remnants of previous regimes, and of the ways in which tourists engage with such presentations. We also discuss one more strategy of dealing with troublesome statuaries which does not involve creating a heritage site: that of destruction.

The monumental statues of our study, created under a now delegitimized political system, form "a memory of waste" (Crane, 2000: 28) and now present as discarded objects of past regimes and toppled despots. All museums and heritage sites are based on "fragmented, dismembered, isolated, de-figured and disjoined objects" (ibid.: 34); they are deliberately disfigured and displaced as if to confuse the ghosts of memory. The parks examined here offer a curated reading of this disposal, of the disposed/deposed and disowned. Heritagization of the stone bodies as survivors of the first wave of destruction being put out to grass transforms them even more fully into memory objects. Their solid and giant forms have been mobilised to their new site beyond the everyday gaze, just as the bodies of tourists and locals who come to see them move to the monuments. Cutting the statues "down to size" in the various approaches under consideration here, takes away or diminishes or manages the potentially strong emotions surrounding memories [START_REF] Wulff | Introduction: The cultural study of mood and meaning[END_REF] such as anger, grief, admiration and fear. The taming or erasing of both political and personal threat is clearly important for sustaining peace in the political present and also for making tourist attractions and spaces comfortable for visitors, even as the emotional life of other cultures and past political regimes sparks interest, curiosity and potentially empathy in tourists [START_REF] Heelas | Emotion talk across cultures[END_REF][START_REF] Tucker | Empathy and tourism: Limits and possibilities[END_REF].

It is a truism to note that the scale and the solidity of public monuments serve to create an aura of permanence and imperviousness to any change enacted in a human timeframe. Their actual lifespan and continued significance is more problematic. A number of strategies have been employed to deal with outmoded or rejected messages these statuaries or other public monuments might be understood to carry, and to find meanings and contemporary context able to accommodate them. The four item typology presented below does not constitute all the possible responses, nor does it cover all of the nuances within each strategy, but can serve as a preliminary analytical tool for understanding and discussing the broad range of possible fates befalling once potent symbols of the rejected past.

Destruction

The first, and most obvious, strategy is destruction: physical obliteration of a monument can serve both to actualize rejection of the originally ascribed meaning, and to prevent unwelcome message from further propagation (continued physical presence might imply continued rhetorical presence). Acts of destruction and defacement often predate political change, or even signal arrested attempts at promoting such change. Thus, the statue of Soviet secret police founder Feliks Dzierżyński in Warsaw was defaced multiple times in the communist era. More recently, many statues connected to racial discrimination, from the slave merchant Edward Colston in Bristol, United Kingdom, through multiple Confederacy-linked figures in the United States, to white abolitionist Victor Schoelcher in Fort-de-France, Martinique have been toppled or defaced in acts of protest.

More significantly, revolutions or dramatic political shifts are marked by symbolic destruction of previous regime's cherished monuments. The demolition of the same statue of Dzierżyński in November 1989, of Lenin statue in Kiev in 2013, and of the monument to Saddam Hussein in Baghdad in 2003 are all celebrated as significant symbolic moments witnessing political change, commemorated through widely disseminated photographs and mediated and re-lived as part of the reinforcement of change. Contemporary global audiences and subsequent generations access these celebratory images and continue to be influenced by them.

In some cases, the act of destruction might itself be felt to warrant commemoration beyond graphic depiction. Thus, during the 1956 Hungarian Revolution, a monumental statue of Joseph Stalin in Budapest (erected only three years earlier) was torn down, leaving only a pair of bronze boots on a ten-metre plinth. These were later removed together with the base of the statue, but, in 2006, a new monument depicting a pair of boots atop a tall pedestal was erected in Memento Park, Budapest, to commemorate the event. We believe it is the only permanent monument created specifically to celebrate the act of statue destruction.

Outside of the revolutionary moment, however, the destruction of statues and monuments is much more problematic [START_REF] Poria | Attitudes and willingness to donate towards heritage restoration: an exploratory study about Bulgarian socialist monuments[END_REF]. Public discourse more commonly celebrates conservation rather than destruction (cf. the rapidly growing list of currently 1121 UNESCO World Heritage sites). There is a tendency for conservative bodies to advocate for conservation [START_REF] Poria | Attitudes and willingness to donate towards heritage restoration: an exploratory study about Bulgarian socialist monuments[END_REF] which implies sustainability of material evidence of pastness. There is a point to be made that conservation can be, and in the case of UNESCO often is de-politicizing at least in intent. Heritage, and world heritage in particular, offers a political overlay of imagined value beyond the political and beyond the local context, making the sites conserving politically contentious or subversive objects worthy of particular attention.

Removal or demolition of monuments commonly encounters protests and condemnation, not necessarily from proponents of their original rhetorical interpretation. Global protests are often about destruction in the abstract, not really the local story. Ultimately unsuccessful international protests regarding the destruction of Bamiyan Buddha statues by the Taliban regime in 2001 remain the most obvious exemplar, but acts such as the removal of the Monument to Brotherhood in Arms (depicting Polish

Delegitimization

Consequently, revolutionary fervour rarely brings about the effacement of all monumental traces of the previous regime, and the strategy of destruction is much less commonly followed in times of political stability. Instead, a second strategy, that of delegitimization, offers another way of dealing with markers of the recently rejected past. It involves diverse activities undermining the perceived rhetorical thrust originally espoused by the monument. At its simplest, an explanatory plaque can add a contemporary commentary while retaining original framing. Usually, more elaborate changes are deemed necessary. [START_REF] Kattago | War memorials and the politics of memory: The Soviet War Memorial in Tallinn[END_REF] chronicles the changes to the Bronze Soldier, a large statue in Tallinn with changing official designation and legitimacy. Erected in 1947 and designated the "Monument to the Liberators," the statue commemorated the taking of Tallinn by Soviet troops in It was later adorned with a continually burning torch. After Estonia's secession from the Soviet Union in 1991, the dominant discourse shifted to understand the event as occupation rather than liberation. The monument was retained as it marked a burial site of Soviet soldiers. However, it was renamed "To Those Killed in the Second World War," the torch was removed, and some of the inscriptions were changed. Nevertheless, the statue remains controversial and any rise in tensions between Estonia and Russia rekindles discussion of whether further changes are needed. Political sustainability calls for decisions to be taken that seem to serve the present.

Large political monuments tend to be situated in significant and prestigious settings and to dominate and organize their spatial surroundings, with framing often chosen to enhance rhetorical appeal. Consequently, delegitimization tends to involve removal to less salubrious locations. The Bronze Soldier statue was itself relocated to less prominent location in 2007, sparking further protests. Memento Park in Hungary, a statue park situated on the outskirts of Budapest, serves as an emblematic case. Established in 1993, it was originally envisioned as an exhibition of totalitarian art from Nazi and Soviet regimes. Ultimately, only half of the original project was completed, and the park showcases only communistera monuments. It largely follows the original layout and presentation, with minor subsequent changes. The flat exhibition area, screened by a brick wall and hedges, collects some three dozen sculptures and sculpture groups (the site's own sources count 42 artworks). Statues are placed without consideration to original positioning or intended presentation: many of the monumental sculptures, in particular, are placed without plinths at ground level, nullifying any relation of awe. Indeed, the disrupted sense of scale appears to invite playfulness, even mockery. Identifying descriptions for the statues themselves are sparse, but framing is provided through other means. The park's website (subtitled: "the biggest statues of the cold war") offers a mixture of different tones and possible interpretations. These include photos of tourists posing with statues (Light, 2000a), commendatory quotations from Hungarian political figures and historians praising the park's value and presentation ("an example for solving a controversial problem in an intelligent and elegant manner"), and sample lesson plans for pupils of different ages (only in Hungarian). Topics range from charting the rise of communism to identifying art styles. and.

Tourist photos open up a theme of mockery: people mimicking the statue poses, jumping around, pretending to high-five the giant monuments. Dancing with despots becomes a legitimate visitor activity, and the appropriate response to the spent rhetorical force of the exhibited statues. The jocular approach is continued by the reception/shop display on the site itself: a mashup poster shows Lenin giving the site a facebook "like" (and invites the reader to do likewise), and items for sale include light-hearted parodies of communist slogans and socialist-realist imagery.

Nevertheless, the largely foreign visitors we have observed and interviewed treated the visit much more seriously: as a learning experience, immersion in the region's past, broadening their horizons. While a few struck relatively timid poses for photos with the statues, for most tourists a visit consisted of walking among the statues, reading plaques and gazing at the monuments. Thus, the strategy of deligitimization, which presents statues as rhetorical objects of the political milieu in which they originated, but with the validity of their message is denied, subverted, or explained away, is only moderately successful in co-opting tourists to produce a sustained narrative of the past. Mockery relies on strong relationship with the object of mockery, and at the present distance from the fall of communism, most visitors approach it as a largely unfamiliar period in history, tinged with generalized respect for the past suffering of the local population [START_REF] Light | Gazing on communism: heritage tourism and post-communist identities in Germany, Hungary and Romania[END_REF].

Decontextualization

At the time of the park's creation, the interpretation of statues primarily as carriers for rhetorical and political messages was the predominant one, at least for the local populace. It is never the only possible reading, though, and its pervasiveness can wane over time. The park's visitors whom we interviewed between 2016-19 showed interest in statues as works of art (or, at least, as representatives of a particular artistic style) and emblems of a historical epoch rather than as political creations.

Vabamu Museum of Occupations and Freedom, a recent history museum in Tallinn, originally opened in 2003. In its original staging of the permanent collection, the curators placed two large statues of Soviet era dignitaries in the underground passage leading to the lavatories, effectively positioning them in the symbolically degrading role of toilet guards. During a 2017 renovation, these statues were removed, and the general emphasis on countering or debunking communist propaganda was lessened throughout the exhibition.

This change is consistent with the third strategy for past monuments: decontextualization. It involves stripping of the original meanings and associations from the monuments, without any corresponding attempt to fix alternative readings. It requires no shared understanding, and no common political standpoint uniting the curators and the visitors, but provides little in the way of guidance as to the value of the presented works, be it artistic or didactic. Decontextualized presentation can accommodate difference in viewpoints among the visitors or conflicted feelings regarding previous political regime(s).

Grūtas Park, a statue park near the small town of Druskininkai in Lithuania exemplifies it well. Created in 2001 by a local entrepreneur, the park exhibits 86 statues (mostly life-size or larger) in a landscaped forest. It also houses a small zoo, with some animals wandering freely around the statues. The site's website proclaims its aim to provide an opportunity for Lithuanian people, visitors coming to our country as well as future generations to see the naked Soviet ideology which suppressed and hurt the spirit of our nation for many decades (Grūtas Park, n.d.) However, if this was indeed the intention, there is little evidence of it in the presentation of the statues themselves. Explanatory plaques describe, in very neutral terms, the subject of each sculpture, as well as the name of the sculptor. The leafy surroundings and secluded location contribute to the peaceful atmosphere of the place, while grazing alpacas set the space apart from the everyday. Grūtas Park is not a popular destination, and during our one day of fieldwork at the site in May 2016 we did not encounter any local visitors. The few international tourists we have interviewed reported bafflement by lack of context or explication. Thus, the strategy of decontextualization should probably be viewed as transitory, providing space and time for new contexts and new interpretations to arise [START_REF] Light | Gazing on communism: heritage tourism and post-communist identities in Germany, Hungary and Romania[END_REF]. Although both Memento Park and Grūtas Park potentially serve the same aims and likely audience, both were clearly created with different agendas. Memento Park denies or defies the logic of time and place through striking juxtapositions of its statues, but it is a carefully structured and contained site. Grūtas Park, in contrast, seems deliberately eccentric and it is not clear whether the elements such as the zoo animals and play parks were added to make the park a "good day out for all the family" or as a conscious statement about the political past. Information boards at the entrance to the park introduced the owner and presented the park as his project, but provided little guidance regarding his curatorial aims. As visitors ourselves from different cultures, countries and political backgrounds we, like the few tourists viewing the site, walked out unsure and confused.

Depoliticization

The final strategy, that of depoliticization, represents an emergence of a new interpretive scheme. It focuses on presenting statuaries as artworks or historical markers rather than as symbols of a political ideology. The focus shifts back onto the objects, rather than on the political system enabling their creation. Such presentation can be found in the sculpture garden of the Estonian History Museum in Tallinn. The relatively modest space, located behind the museum itself, houses 21 different Soviet era sculptures, arranged in a rough circle. Descriptive plaques focus on the sculptors and art styles, similar to how other works of art are presented elsewhere in the museum context. This is by far the smallest of the sites we have viewed, but in many ways the most informative-its compactness allows visitors to compare and contrast different iterations of the Soviet era socialist-realist style . It is also the newest site: laid out in its present form only in the 2010s, and the least politically-charged: the sculptures appear primarily as artistic creations of individual sculptors, albeit working in a specific time and place.

The visitors exhibited a variety of behaviours, from hurried passage, through thoughtful appreciation, to playfulness or mockery; there was no clear approved script for them to follow. Like the interviewees we spoke to in Memento Park, visitors here viewed the statues as object from a bygone era rather than as participants in an ongoing political struggle.

Discussion

Our interest here is twofold. Through examining how nations and communities deal with symbolic structures of monumental statuaries to move forward politically and emotionally from the events of recent past, and to support individual, collective and national remembering allowing for sustainability within the political present and future. Multiple viewpoints and potentially contentious and competing memories and narratives are not readily known or accessible and our fieldwork frames the studied sites as meeting points for remembering and forgetting both within and beyond the heritagized spaces. We also query the role and impact of tourists in shaping the heritagized visions and version of the past within the sites and the extent to which the studied sites have been shaped to encourage tourism supporting the fixing of such narratives despite a seeming lack of interpretation for tourist audiences.

Who visits?

All of the above key sites are essentially outward-facing. They actively encourage tourists and seem specifically marketed as tourist attractions. Lehrer and Milton (2011: 5) rightly challenge terms such as dark tourism being applied to visits to sites associated with painful pasts as they note that while such visits "raise concerns about voyeurism and crass commercialisation, they may just as often draw people earnestly seeking to mediate on peace, imagine common futures, and even forge these through dialogue or political action".

An interesting issue is how locals and tourists, often coming from different backgrounds, counties and cultures, perceive sites such as Memento and Grūtas Park set up in peripheral zones to contain the figureheads of past regimes. These are displayed and curated as both collectively banished and creatively presented. This act of banishment is the one thing they share in the present. Collectively, they are offered up as political waste in a political wasteland (Wallis, 2019).

Feldman reframes Clifford's notion of "museums as contact zones " (1997: 192) arguing to substitute conflict for contact: zones where inequalities meet; this (re)reading forces a reassessment of heritage spaces. Analogically, places like Memento and Grūtas Park constitute meeting sites where tourists and local visitors alike have to negotiate these constructed placeless places. Lehrer and Milton (2011: 7) argue that representation of recent past constitutes "attempts to curate difficult knowledge" within the framework of "transitional justice," drawing on symbolic objects and spaces of the past to render the present less contentious and more acceptable. States, nations or communities work to reclaim and reject ideologies and their symbolic markers both within the geographical sphere -landscapes of memory -and as objects associated with such landscapes. [START_REF] Hartmann | Fragmentation and forgetting: Sarajevo's Vijećnica[END_REF] notes that formal heritage spaces can support the erasure of collective remembering and Mitchell (1992: 30) adds that the pulling down (and we might add, re-placing) of public art "is as important to Article published online (2021) in Journal of Sustainable Tourism. Publisher version DOI: 10.1080/09669582.2021.1909602 its function as its putting up". The framing of statues in themed spaces merges the forms of museum (generally emphasizing material culture and the "real"), heritage constructions as politic (Ashworth, 2008) and the wholly experiential "theme park" spaces created rather than curated as other worlds. In the latter, sensemaking is framed by inauthenticity and also potentially edutainment [START_REF] Balloffet | From museum to amusement park: The opportunities and risks of edutainment[END_REF][START_REF] Babic | Bridging the boundaries between museum and heritage studies[END_REF], setting the atmosphere for the experience [START_REF] Bonn | Heritage/culture attraction atmospherics: Creating the right environment for the heritage/cultural visitor[END_REF].

Visitor responses: correct or expected?

Visitors respond to sites that present difficult knowledge according to their own understanding of and relationship to the past [START_REF] Carnegie | Occupying whateverland: journeys to museums in the Baltic[END_REF]. Such sites reinforce understanding of the past and offer continuity in terms of historical "truths" or at least narratives of events and place. As Lehrer and Milton (2011: 9) note, both tourists and local community visitors' emotional responses to exhibitions change over time as people "unevenly engage with the processes of 'working through' in relation to their communal tragedies". Historic events and their mediated representations or exhibitions that follow become solidified as accepted formal versions of the past shaped for contemporary audiences [START_REF] Silverman | Visitor meaning-making in museums for a new age[END_REF]. Individual and community remembering and tourist knowledge may challenge perceived constructions of past events focusing on significant points that shape or aim to define formal remembering as opposed to the lived experience of individuals or the formal teachings received by tourists in another political context. How these representations are received and perceived depends on where, how and importantly when visitors developed their knowledge and values of the past being depicted. Importantly for this study, we, as curators, locals, visitors and academics, witness the emergence of images and objects from their challenging original context into the "visible, material touchstones of new experiences and narratives" (Lehrer and Milton, 2011: 17).

One of the key ways of rendering objects harmless is to change the context for their remembering. Simon (2011: 207) discusses the need for a "pedagogy of witnessing" where the past and present can be represented "without reducing one to the other, or dictating the terms on which this is to be accomplished". This call for ethical or moral curating denies, obviously, the political, social and economic acts that brought about the changes in society either through violent acts or by peaceful means. Individuals do not curate their own memories although they may build up collective memory banks within their localities, but only where it is safe or desirable to do so. Otherwise, memories which challenge the "desired" formal narratives or are too painful go underground or are subject to selective self-banishment.

Museums and heritage spaces collect and reframe objects in order to give them sense in the present. This suggests that curators present objects in a way they understand as best suited to contemporary audiences. Social, cultural and political changes, fashion and geography all influence these interpretations. Notable examples include the "New Museology" debates largely focused around accessibility representations, and more recent attempts to frame the post-modern museum as a more knowing and known space [START_REF] Stam | The informed muse: The implications of 'The New Museology' for museum practice[END_REF][START_REF] Dwyer | Memorial landscapes: Analytic questions and metaphors[END_REF]Zhong et al., 2018). As Watson (2007: 4) argues, all curated sites have some sense of being part of a local or regional community or of serving national narratives.

Museums and heritage site representations follow certain curatorial approaches; these tend towards chronological, geographical, thematic and aesthetic or a mixture of these [START_REF] Simpson | Making Representations: Museums in the post-colonial era[END_REF][START_REF] Bennett | Stored virtue: Memory, the body and the evolutionary museum[END_REF]Stonger, 2009). Visitors need to understand curatorial logic to be able to negotiate spaces and effectively engage with them [START_REF] Hennes | Exhibitions: From a perspective of encounter[END_REF]. We contend that Memento and Grūtas Parks defy the logic of association with place and are chronologically and literally "all over the place". Sensemaking is therefore limited to an understanding of the relationship of each of the figureheads depicted in the statues to one another. What they all have in common is that they reflect a past political regime. This deliberate juxtaposition reduces them to that of just past political figures although some have no geographical link to the localities they are now in and some were clearly important political forces such as Lenin. Some were the works of the best artists and sculptures of the period, others more roughly cast where the representation and not "artistic merit" was required. The works in Memento Park are displayed as in a temple, in Grūtas Park a grotto within a zoo. This deliberate loss of usual curatorial sensemaking and the seemingly provocative and confusing display strategies, are at once playful and mocking and immersive in their creation of imaginary. They result in presentations that reflect [START_REF] Bencard | Presence in the museum: On metonymies, discontinuity and history without stories[END_REF] world of "history without stories". Williams (2007:8) defines a monument as "a sculpture, structure or physical marker designed to memorialise". He claims that "a memorial is seen to be, if not apolitical at least safe in the refuge of history", as it capitalizes on respect our culture demands to be given to all dead. But disrespect, as we have shown, can also appear as an early, engaged response to political change, a way of moving beyond the all-or-nothing decisions on how to treat markers of significant suffering, with the usual options being obliteration or sanctification (Williams, 2007: 185). The monumental statues forming the core of our study are not, generally, witnesses to atrocities or immediate markers of suffering. They are seen, however, as glorifying, directly or indirectly, an oppressive regime whose vanquishing forms the founding narrative of the current political system, and the first three strategies for dealing with disgraced statues invite tourists to participate in creating or emphasizing the point of rupture at the end of the previous regime.

Yet, as Nadkarni (2003: 196) notes, the demise of socialism "did not represent revolution, but the end of the age of revolutions" and came about largely peaceably despite representing a point of rupture. She adds that the "communist monuments had inspired not only anger, but also indifference, irony or affection" (ibid.: 198). The initial argument for Memento Park embodied a compromise between proponents of immediate destruction of communist-era and those willing to keep them in situ. Statues' preservation was deemed an "emblem of democracy" which allowed insights into "aesthetics, ideology and historical politics of the previous era" (ibid.: 198). She notes that some protestors considered the park a "human zoo" and an anti-democratic act of dismissing varied contexts and significance of different statues. In particular, the statue of the Soviet soldier Osztapenko, erected on a route leading to the popular holiday spots, functioned primarily as a place marker and not a political symbol. The same example was brought up (without prompting) fourteen years later by one of the local visitors to Memento Park whom we interviewed. Nadkarni further noted that while "countless Lenins proved the fact of Soviet occupation, it was perhaps even more pressing to remove Osztapenko, who called attention to the ways forty years of Socialism had become cosy and familiar" (ibid.). Memento Park's opening in 1993 coincided with the second anniversary of the removal of communist troops from Hungary, and Nadkarni notes the irony in the way the event was reported in the Western press as a money-making venture, presenting communist statues as reformed servants of the new capitalist economy. This, and the site's marketing appealing to international tourists through socialist realist kitsch, provided for the early visitors an interpretive framework that "offered proof of both the oppressed Socialist past that feared and hated these statues and the democratic present that is free to laugh at them" (ibid.: 203). However, contestation does not necessarily come from "conflicting accounts of what actually happened in the past… as much as the question of who or what is entitled to speak for that past in the present" (Hodgkin and Radstone, 2003: 1). Instead, the "past is constituted in narrative, always representation, always construction" (ibid.: 2). Heritage spaces constitute a particular form of formal remembering, selectively framing the past to suit the political needs of the present: the past represented through disgraced statues is used to highlight ruptured continuity and momentousness of political change. But personal memories are contradictory, flawed and complex with the potential to challenge, corroborate, and intertwine with the formal narratives of place. The Budapest locals whom we have interviewed in relation to Memento Park still associate the individual statues in their original setting, as part of their own memories: as former meeting points and other memory markers.

Memorials embody a historical "return of the oppressed" (Kapralski, 2011: 187), and thus invite unambiguous demarcation of the categories of the oppressed and the victims. But, intricateness and contradictions of history and of memory give monuments irreducible complexity. Sites such as Memento Park or Grūtas Park defy easy characterization as a failure, commercial enterprise, or a tourist site; they function as places where memories are gathered interpreted differently by different stakeholders. That they are also places that many locals we spoke actively choose not to visit is yet another of their roles.

Tourists as supportive peacemakers

This leads us to consider on-site tourist behaviours and how they support the wider aims of the parks in the present. Are their responses in keeping with the overall tone of the parks which is more mocking than reverential, chaotic in the mix of statues from time and place, artistic quality and local significant? Our initial thoughts on our first visit to Memento Park fixated on the purely human response to the scale of the works there, as we witnessed some of the visitors climb the monuments, pose and "dance" with them, leading to our titular metaphor of dancing with despots. We thought of tourists performing as proxies for local visitors who may chose not to visit. But the act of mocking evident in the dancing and general playfulness, they were giving an appropriate repose, disrespecting the statues and therefore participated in creating rupture from the ideology and regime that they stood for. We still hold this interpretation as valid, but also as incomplete.

Formal narratives and representations of the political past confined and contained as a heritage park are relatively straightforward. Meanwhile, the range of emotions felt by those for whom they formed part of the everyday lived experience and the subsequent generations for whom the park represents Bell's (1997: 827) "unsettling ghosts of place" remains complex and unruly. Tourists may indeed have an imagined ideal role in sustaining the present through seemingly mocking the past, but only in the sense that by appearing to do so they may serve formal political narratives.

Having conducted fieldwork at a ten different sites as part of the project (including the three described in more detail in this text) we argue that tourist responses, and in particular Western international tourists, are also complex, and influenced but not determined by the context of the space, and the desire to learn and understand. Through interaction with sites tourists sustain and challenging their own "knowledge bank" of what they learned about this period of time and what they can then witness. We argue that a more thoughtful tourism develops to reflect this complexity.

However, reflexive engagement with heritage sites can be an uncomfortable, even painful experience, depending on the visitors' relationship to the presented past [START_REF] Poria | Attitudes and willingness to donate towards heritage restoration: an exploratory study about Bulgarian socialist monuments[END_REF][START_REF] Carnegie | Occupying whateverland: journeys to museums in the Baltic[END_REF]. Moreover, complexity and ambiguity are both difficult to convey to visitors unfamiliar with the context, and often problematic for the curatorial teams socially, ideologically, and politically engaged in potentially unstable milieus. We would also recognise that in conducting our fieldwork, we actively invited visitors to reflect on both their understanding of the context of the parks and their feelings about them. This can have served to evoke feelings and insights which would have not been part of their experience without us present, but the thoughtful responses we received also suggest that reflexivity can be a welcome part of the visitor experience.

Tourists interviewed as part of this project came as thoughtful visitors, aware of the key moments of recent history. However, they did not necessarily know how to "read" the site in terms of expected behaviours. The ticket booth at Memento Park sells ice-cream and souvenirs which are parodistic and aimed at Western tourists (a tin that contained the "last breath of communism", ironic posters). Similarly, Grūtas Park is a confusing space, part zoo, part heritage park where animals graze among statues. The inference is that sculptures are now part of a human zoo, tamed, controlled, if not endangered. This show of levity gives visitors permission to mock, to joke and as the title of this article suggests, to dance among the despots.

In many ways, this challenges the idea that tourist to such sites are necessarily deferential, yet it does not equate to a deliberately mocking or disengaged form sometimes associated with dark tourism. Rather, the confused response should be recognized as the desired behaviour for encountering and assimilating the complexity of history. As North (1990: 861) notes, "changing the nature of the art means changing the role of the audience as well… as the aesthetic shifts from the object to the experience it provokes".

Conclusion

Armada (2010) argues that when one memory is prioritised, other memories are executed. However, our study suggests memory is complex and nether linear nor permanently erased or erasable just as the symbolic structures of memory -the monumental statuary can be erased yet remain in popular and public memory [START_REF] Dresser | Set in stone? Statues and slavery in London[END_REF][START_REF] Goodrich | What are statues good for? Winning the battle or losing the battleground?[END_REF]. The parks may form a bridge between the past and present values, or may be consciously reframed in the present. Our research determines that the absence of interpretation within public spaces should not be viewed as forgetting or even as deliberate attempts to hide the past [START_REF] Armada | Memory's execution: (Dis) placing the dissident body[END_REF]. And Grūtas Park shows that seeming neutrality in interpretation does not necessarily or ever suggest neutrality of behalf of the organiser.

Less political and arguably more reflective ways of treating the material have been emerging more recently: the art-historical responses of the strategy of depoliticization [START_REF] Drayton | Rhodes must not fall?[END_REF][START_REF] Ranja | Heritage of the Finnish Civil War monuments in Tampere[END_REF]. The same statues previously displayed in Tallinn under the name of a statue graveyard are now presented as a floodlit outdoor art gallery without an overt call to a mocking or condemnatory response. Thus, sustaining the political present becomes both easier and harder over time -easier as memories become less acute, harder because a new form of disillusionment about current regimes and nostalgia comes as a consequence of passing of time (Light, 2000a). Political swings equally threaten the political status quo, and both retention and removal of past symbols can create different resonances in different contexts. North (1990: 861) argues that "sculpture becomes public by taking the spatial experience of its audience as a subject." The resulting "cultural space" becomes a meeting ground for both agitation [START_REF] Tunbridge | Difficult Histories and Positive Identities[END_REF][START_REF] Hicks | The Brutish Museums. The Benin Bronzes, colonial violence and cultural restitution[END_REF]Ranja and Silva, 2020) and potentially peace making [START_REF] Higgins-Desbiolles | Challenging peace through tourism[END_REF][START_REF] Hautamäki | Heritage of the Finnish Civil War monuments in Tampere[END_REF]. As Farmaki (2017: 538) notes, peace building is not a "static but a continuous process" and tourism can support or moderate positive peace building. The statue parks we studies have evolved into predominantly tourist-facing spaces in which tourists contribute to and support the narrative of achieved peace and historical justice. Visitor-tourists are eager to understand and partake in experiencing historical milieus, ready to accept and internalize curated visions of the past. Memento Park is an established part of the tourist offering in Budapest and although its peripheral siting attracts only those committed to making the journey, it has become a 'known space' popularised through and for tourism and as such has a wider reach than its peripheral siting would suggest. The statue park at the Museum of National History in Tallinnwas already a tourist attraction when a 'statue graveyard' -described as a symbol of rejection, decay and conscious neglect. The move to a formal display heralds the recognition of the importance of tourism in framing the recent past and its reception with external audiences.

Our findings determine that thoughtful tourists have a real and relevant role to play in forming and indeed solidifying narratives of the past. In this we argue, that while representations of the recent past are not always consciously shaped for external and tourist audiences, tourists often form a key audience. At the same time, the local people we interviewed still remember the statutes and where they stood when they pass the actual spaces where they were once erected. As time passes these memories become more symbolic and will sooner or later become folk memories [START_REF] Hartmann | Fragmentation and forgetting: Sarajevo's Vijećnica[END_REF].

This study of statues as monuments to cultural change and changing cultures is topical and timely. Statues are often seen as both focus and pretext for discussion of key figures' role in history [START_REF] Drayton | Rhodes must not fall?[END_REF]. At present, statue parks are both places of fragmented memory and forgetting. Folk memories blur timelines and can become both a threat to and evidence of acculturation as narratives change and shift over time. Managing these processes of change becomes part of the successive governments' necessary strategic agendas to maintain the political status quo [START_REF] Ashworth | Heritage, identity and Europe[END_REF][START_REF] Hicks | The Brutish Museums. The Benin Bronzes, colonial violence and cultural restitution[END_REF]. In this sense, tourists' engagement with statue sites helps support and maintain a consensus fixing the narratives of the past, and thus contribute, steadily rather than spectacularly, to stability and peace through tourism.

  Dances with Despots: Tourists and the afterlife of statues Article published online (2021) in Journal of Sustainable Tourism. Publisher version DOI: 10.1080/09669582.2021.1909602 and Soviet World War II soldiers) in 2011 also merited strong opposition.

  Article published online (2021) in Journal of Sustainable Tourism. Publisher version DOI: 10.1080/09669582.2021.1909602


Detlef Lohse
email: d.lohse@utwente.nl

Emmanuel Villermaux

Double-threshold behavior for breakup of liquid sheets

When being outside in nature in the presence of cold, windy and rainy weather, most of us will have wondered: How do birds keep themselves warm? Not only does the wind imply a thinner thermal boundary layer over bodies, favoring heat loss, but in addition the impacting raindrops add considerably to the cooling, directly taking heat away, as most of us will have experienced, when being outside and unprotected in a heavy shower. Birds are better off in such a situation: To partly protect them against the heat loss from impacting rain droplets, evolution has equipped them with feathers, which have a hierarchical superhydrophobic structure. As Kim et al. have now shown [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF], one function of this structure is to minimize the contact time between falling drops and the bird, in order to minimize the net heat transfer. In addition to droplet impact experiments on feathers, the authors studied droplet impact on butterflies and leaves, which also possess hierarchical superhydrophobic structures, as well as on such structures that were manufactured in a controlled way.

The water-repellent character of superhydrophobic leavesthe so-called lotus-effect -has been well studied ever since the pioneering work of Barthlott and Neinhuis [START_REF] Barthlott | Purity of the sacred lotus, or escape from contamination in biological surfaces[END_REF]. However, the focus of this line of research has been on gentle droplet deposition on the superhydrophobic structures, and not on droplet impact with large inertia ρU 2 compared to the capillary confinement by surface tension forces γ/R, in other words, previous work has not focused on large Weber numbers W e = ρU 2 R/γ, where U denotes the impact velocity, R the droplet radius and ρ and γ are the density and surface tension of the liquid, respectively. In contrast, the focus of the new droplet impact experiments by Kim et al. [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF] on hierarchical superhydrophobic structures is on the large W e regime.

One of the first studies on large Weber number drop impact on micro-and nanostructured superhydrophobic surfaces was by Tsai et al. [START_REF] Tsai | Droplet impact upon micro-and nanostructured superhydrophobic surfaces[END_REF], who found a transition from bouncing to splashing with increasing W e. For the structures they employed, this transition occurred around W ec ≈ 120. Thanks to their ability to manufacture transparent hierarchical superhydrophobic structures and thus allowing for bottom views, Kim et al. [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF] could now elucidate the nature of this transition. The bottom view allowed them to define and measure the contact time of the droplet, extended in the form of a circular sheet, with the substrate.

For their hierarchical superhydrophobic structures, beyond W ec ≈ 150 they found a transition towards considerably reduced contact times of the droplets (see Fig. 5c of [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF]). In that large Weber number regime W e > W ec the contact time becomes much smaller than the capillary time τ ≈ 2.3 ρR 3 /γ, which is otherwise an excellent estimate [START_REF] Richard | Contact time of a bouncing drop[END_REF] for the contact time when W e < W ec, independent of U . In addition, Kim et al. [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF] found that for W e > W ec, the contact time decreases with further increasing W e.

In the experiments by Kim et al. [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF] the transition between the two W e-regimes only occurs for impacts on hierarchical superhydrophobic structures, and not for impacts on a smooth surface. Compare the bottom view snapshots for the drop impact for W e = 680 > W ec on a smooth surface (figure 2a of [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF] at 1.9 ms) with that on the hierarchical superhydrophobic structures (figure 2c of [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF] at 4.2 ms): While in the former case a stable sheet is seen, which after maximal extension pulls back, in the latter case the hierarchical structures of the surface break the sheet up through the nucleation of characteristic holes, which quickly expand. Such hole opening dynamics in a liquid sheet has been associated with the names Taylor and Culick [START_REF] Taylor | The dynamics of thin sheets of fluid. III. Disintegration of fluid sheets[END_REF][START_REF] Taylor | On making holes in a sheet of fluid[END_REF][START_REF] Culick | Comments on a ruptured soap film[END_REF] and the opening speed -the so-called Taylor-Culick velocity 2γ/ρh -diverges when the thickness h of the liquid sheet vanishes.

In the Kim et al. [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF] experiments, the emergence of the holes can only happen provided (i) the sheet is thin enough, i.e., for large enough spreading, implying a large enough W e, and (ii) that here is a large enough distortion on the liquid sheet, which here is provided by the roughness of the surface on which the impact takes place. In order to rationalize these findings, the authors provide an ad-hoc analysis invoking capillary waves interacting with the distorted landscape of the solid surface, resulting in a simple hole nucleation criterion: For given surface roughness amplitude , the critical impact velocity is Uc ∼ γ/ρ , independent of the droplet radius R, implying W ec ∼ R/ , independent of the type of liquid. This analysis accounts for the experimentally observed double threshold behavior for sheet breakup: (i) Strong enough driving and (ii) large enough distortions. series of liquid films impacted by a shock wave at Mach numbers M = 1.07 pierced by holes colliding to form a web of ligaments [START_REF] Bremond | Bursting thin liquid films[END_REF]. (d) A network of holes punctured by bubbles in a water radially expanding sheet shown at two consecutive instants. [START_REF] Lhuissier | Effervescent' atomization in two dimensions[END_REF]. (e) Holes on a water sheet punctured by oil droplets dispersed in the liquid [START_REF] Dombrowski | A photographic investigation into the desintegration of liquid sheets[END_REF].

Reserved for Publication Footnotes

The sheet breakup mechanism studied by Kim et al. typifies a whole class of sheet breakups occurring in nature and technology. E.g., the liquid sheet breakage occurring after a flying liquid drop was hit by a strong laser pulse [START_REF] Klein | Drop fragmentation by laser-pulse impact[END_REF] shows quite some similarity, see Fig. 1a. Again, a double threshold behavior is found: (i) The Weber number must be larger than a critical Weber number (W ec ≈ 170, see [START_REF] Klein | Drop fragmentation by laser-pulse impact[END_REF]) and (ii) the distortions must be sufficiently large, here provided by spatial inhomogeneities of the laser pulse.

A situation which is even closer to that of Kim et al. [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF] is the one of droplet impact on a superheated surface, leading to the so-called Leidenfrost effect, where the droplet floats on its own vapor [START_REF] Quéré | Leidenfrost dynamics[END_REF]. Again, also in this case there are two regimes: For the static Leidenfrost effect [START_REF] Quéré | Leidenfrost dynamics[END_REF], the drop is gently deposited on the superheated surface (i.,e., very low impact ve-locity) and then hoovers around, slowly evaporating. Also for the dynamic Leidenfrost phenomenon [START_REF] Tran | Drop Impact on Superheated Surfaces[END_REF], where the droplet impacts a superheated surface, it remains intact, provided the impact velocity is not too large. However, beyond a critical impact Weber number W ec, the droplet spreads so much over the superheated surface (without touching it) that the liquid sheet becomes so thin that holes emerge and grow [START_REF] Staat | Phase diagram for droplet impact on superheated surfaces[END_REF][START_REF] Shirota | Dynamic Leidenfrost Effect: Relevant Time and Length Scales[END_REF]. This regime is called the film-splash regime; the critical Weber number W ec beyond which it occurs depends on the surface temperature and is of the order of 100 -200, see Fig. 5 of [START_REF] Staat | Phase diagram for droplet impact on superheated surfaces[END_REF]. A typical case for the film breakage in the film-splash regime of the dynamic Leidenfrost phenomenon is shown in Fig. 1b, which very much resembles figure 2c (at 4.2 ms) of ref. [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF]. Presumably, the liquid vapor under the film provides enough distortions to the liquid film so that it can eventually break for W e > W ec. What could contribute to these distortions are thermal inhomogeneities, leading to thermal Marangoni flow, or local vapor bubble bursting, among other possible causes, see below. So also here a double threshold behavior may be in place.

The combined effects of surface structure and superheating on the disintegration of the emerging liquid sheet were also studied [START_REF] Tran | Droplet impact on superheated microstructured surfaces[END_REF][START_REF] Nair | The Leidenfrost temperature increase for impacting droplets on carbon-nanofiber surfaces[END_REF]: Thanks to the massive production of vapor under the liquid sheet at the rough and hot surface, a strong radially outwards flow develops which helps the sheet to radially spread, leading to much earlier sheet breakage, both as compared to the rough and cold case [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF][START_REF] Tsai | Droplet impact upon micro-and nanostructured superhydrophobic surfaces[END_REF] and to the smooth and hot case [START_REF] Staat | Phase diagram for droplet impact on superheated surfaces[END_REF].

Again, in all these cases two conditions must be fulfilled for the liquid sheet to break: (i) The inertial driving of the sheet must be strong enough as compared to the surface tension keeping the liquid together, i.e., the Weber number must be large enough, and (ii) there must be a large enough initial distortion, either externally imposed, or internally sustained by an instability.

But what do we know for all these cases about the actual film breakage mechanism? The criterion found by Kim et al. for when a sheet breaks -a coincidence of length scales (the sheet thickness h versus the surface corrugation amplitude ) -is very valuable, but it does not say anything on the very piercing mechanism per-se: The sheet thinned at the extreme could well coat the surface grooves without breaking, so that the hole nucleation mechanism remains to be elucidated.

There are in fact many ways in which a liquid sheet, or film, may puncture (see the review in [START_REF] Néel | The spontaneous puncture of thick liquid films[END_REF]). A hole will expand provided its diameter is larger than the sheet thickness [START_REF] Taylor | On making holes in a sheet of fluid[END_REF]; otherwise it heals. But the causes of hole nucleation are diverse:

1. Extremely thin films are sensitive to thermal fluctuations. This thermally activated puncture may thus at most apply to films with thickness of order h ∼ kBT /γ ≈ 10 -10 m in water at ambient temperature, like Newton black films. 2. Very thin films, with thickness of the order of a few tens of nanometers are sensitive to van der Waals forces and puncture under the driving force of the disjoining pressure -A/h 3 where A is a Hamaker constant. 3. External forcings may perturb the film to rupture. The collision with a sharp solid object with a radius of curvature smaller than the film thickness, like in the Kim et al. [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF] experiments leads to puncture, as well as the mechanical action of a concentrated air jet, of a focused laser beam or a spark vaporizing the liquid. The stimuli may also result from an instability, like the application of a pressure gradient, or pressure difference across a film. The corresponding acceleration may lead to film thickness modulations through a Rayleigh-Taylor mechanism [START_REF] Klein | Drop fragmentation by laser-pulse impact[END_REF][START_REF] Bremond | Bursting thin liquid films[END_REF][START_REF] Vledouts | Explosive Fragmentation of Liquid Shells[END_REF] i i "pnas-comment" -2020/6/29 -20:24 -page 3 -#3

i i i i i i
ultimately causing its puncture. The same phenomenon is responsible for the crumpling of liquid bells, and the formation of transverse indentations at the edge of flapping liquid sheets [START_REF] Lhuissier | Crumpled water bells[END_REF][START_REF] Lhuissier | Soap Films Burst Like Flapping Flags[END_REF]; it may affect films with thicknesses in the micron to tens of microns range (Fig. 1a,c). 4. Internal flaws and defects like solid hydrophobic particles introduced into a film can, when their size compares with the film thickness, lead to its rupture as they force the two interfaces of the film to pinch at the surface of the particle. Anti-foaming agents have taken advantage of this effect for a long time. Immiscible oil droplets [START_REF] Dombrowski | A photographic investigation into the desintegration of liquid sheets[END_REF][START_REF] Vernay | Bursting of Dilute Emulsion-Based Liquid Sheets Driven by a Marangoni Effect[END_REF], bubbles [START_REF] Lhuissier | Effervescent' atomization in two dimensions[END_REF] also act as efficient hole nucleation sites in water films (Fig. 1d). 5. Chemical and temperature inhomogeneities at the surface of a liquid translate into inhomogeneities of surface tension. The corresponding Marangoni surface stress [START_REF] Marangoni | Difesa della teoria dell'elasticità superficiale dei liquidi. Plasticità superficiale[END_REF] is communicated to the bulk of the liquid by viscosity in a way, when the liquid is shallow like in films, which can be dramatic [START_REF] Scriven | The Marangoni Effects[END_REF]. When the film sits in a transverse temperature gradient, or when surface tension is locally lowered by an impurity (see Fig. 1e) the tangential flow digging the film is amplified, leading to rupture [START_REF] Néel | The spontaneous puncture of thick liquid films[END_REF]. Applications are numerous, including boiling [START_REF] Kabova | Marangoni-Induced Deformation and Rupture of a Liquid Film on a Heated Microstructured Wall[END_REF], surface cleaning [START_REF] Leenaars | Marangoni Drying: A New Extremely Clean Drying Process[END_REF], or the stability of surface bubbles [START_REF] Lhuissier | Bursting bubble aerosols[END_REF][START_REF] Poulain | Ageing and Burst of Surface Bubbles[END_REF]. 6. Finally, kinematic thinning, which results from initial inhomogeneities of the liquid interstitial velocity, an effect that may be involved in the Kim et al. [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF] observations, and which is characteristic of thick, turbulent films, also provokes rupture in finite time [START_REF] Burton | Two-dimensional inviscid pinch-off: An example of selfsimilarity of the second kind[END_REF].

Most of these mechanisms of hole nucleation have a doublethreshold behavior in common.

In a broader context we note that the double-threshold feature of an instability -in the work of Kim et al. [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF] for the spreading liquid sheet, for which both the Weber number and the distortion must be large enough for the instability and breakage to occur, or correspondingly for the other liquid sheet rupture cases we discussed -is rather common in fluid dynamics in general. Other better-known examples are pipe flow or other shear flows where both the Reynolds number and the initial distortion must be large enough for the flow to become turbulent [START_REF] Schneider | Turbulence transition and the edge of chaos in pipe flow[END_REF][START_REF] Eckhardt | Turbulence transition in pipe flow[END_REF][START_REF] Barkley | Theoretical perspective on the route to turbulence in a pipe[END_REF] and where the instability is associated with the interplay between non-normality and nonlinearity of the flow [START_REF] Grossmann | The onset of shear flow turbulence[END_REF][START_REF] Chomaz | Global instabilities in spatially developing flows: non-normality and nonlinearity[END_REF][START_REF] Kerswell | Nonlinear nonmodal stability theory[END_REF], or visco-elastic polymer flows where both the Weissenberg number and the initial distortion must be large enough [START_REF] Morozov | An introductory essay on subcritical instabilities and the transition to turbulence in visco-elastic parallel shear flows[END_REF]. We speculate that the theoretical concepts successfully applied to explore the instabilities of these flows may also be beneficial to better understand the breakage of thin liquid sheets.

Finally, we would like to suggest an application perspective for the work by Kim et al.. In most cooling facilities, the contact between the cooling liquid and the surface to be cooled should be maximal, in order to ensure the best heat transfer. However, a further increase in the heat flux can result in a discontinuous and large increase of the wall temperature, which is appropriately called burn-out or boiling crisis [START_REF] Dhir | Boiling heat transfer[END_REF]. The reason for this behavior lies in the massive formation of vapor bubbles which strongly reduce the direct contact between the liquid and the superheated surface (similarly as in the Leidenfrost state [START_REF] Quéré | Leidenfrost dynamics[END_REF]) and thus to over-heating of the surface, potentially leading to its destruction. However, in the opposite case, namely in applications in which a surface is supposed to stay warm and thermally isolated in spite of being exposed to droplets and spray, the results of Kim et al. [START_REF] Kim | How a raindrop gets shattered on biological surfaces[END_REF] teach us that micro-and nanostructuring the surface can be helpful for minimizing the contact time and thus the heat transfer. For given droplet size and velocity, their estimates provide guidelines as to the roughness length scale that is sufficient to achieve this. That this strategy can work has in fact been proved by birds who happily sit or fly in a cold rainshower without freezing, protected by their hierarchically micro-and nanostructured feathers.

Fig. 1 .

 1 Fig. 1. Nucleation of holes on various liquid sheets: (a) Bursting water sheet which emerged out of a droplet being shot at with a highly energetic laser pulse at W e = 530 and undergoing an impulsive Rayleigh-Taylor instability [12]. (b) Bottom-view of an ethanol droplet of d = 2.52 mm with U = 2.0 m/s (that is We = 420), 6.7 ms after impact on a sapphire surface heated up to 200 o C [11]. (c) Time

ACKNOWLEDGMENTS. We gratefully acknowledge many discussions on the dynamic Leidenfrost effect and hole nucleation in general with Michiel van Limbeek, Henri Lhuissier, Pierre Chantelot, Chao Sun, and Andrea Prosperetti. D.L. also acknowledges financial support through the ERC Adv. Grant "DDD" under grant number 740479 and through MCEC, which is supported by NWO. E. V. acknowledges the Agence Nationale de la Recherche (ANR) for funding of the grant ANR 'FISICS' ANR-15-CE30-0015-03.