A human being who places its
lips upon the orifice of a dog's
asshole and runs its tongue up the dog
hole.
Check out the underground film titled "Variations on a Theme" -- there is a segment called "Rondo Cane" -- in that portion of the film (the last of that cinematic
epic) the dog (a great dane) is on the floor, I go under it's tail and stick my tongue up the
dogs'
asshole as far as it will go.