"Two small dogs, one black-and-white and one brown-and-black, walk down the street."
The black and white dog is sniffing the butt of the brown dog that is on a leash.
A brown and black dog on a leash is sniffed by a black and white dog.
A dog on a leash walks on the sidewalk while another dog follows.
A small dog on a leash is being smelled by another animal.