Bestiality, eh? Hmm, it has bene in some of the stories I've read, but it has never been a major kink of mine <_<. Anyway, might as well put my 2 cents here.

On the subject of a dog being consentual or not, I think that if a dog doesn't want it, then he/she will show it, as has already been said. My family had a dog before back when I was a kid, and althrough he was a nice dog, even he got tired of playing with us kids at times, so when he didn't want to rush around and play with us, he showed it by barking or growling at us, or even give a soft bite on the hand if we were persistent.

As for it being unatural for the dog - come on, for how long have we humans been raising dogs to suit our own purposes rather than the dog's own? . As has been mentioned, it is hardly within the dog's "nature" to be getting newspaper, balls or slippers for us . And how often are we not in some way using the dog's abilities in one way or another? They're fast and have good hunting insicts, so they can become hunting dogs or sheephounds. And their sharp sense of smell is what has gotten us to train them to find stuff like crack, escaped criminals and so on... So who who owns an animal (of a certain kind, since there's exceptations, cats are allowed to keep more of their true nature than some other animals, for example) can't say that he/she aren't twisting the true nature of the animal in some sense?

So overall IMHO bestiality is not that abusive to the animals, but it depends on the situation and how the animal is treated otherwise... Well, that's my 2 cents, that