I saw one with a lobster once, the entire tail inserted...some things are just wierd.

As for consensual, it raises long ethical questions. There is definitely a clear line to abuse and force, but is putting a dog on a leash during a walk consensual? Is yelling at him not to pee there again? Selling off its puppies? It's not my fetish, but let's all pause a moment before we whip out our morality lessons.