My dog has never once ever even demonstrated any kind of biting or nipping to me or anyone else. Over the past few weeks ever since my daughter brought in this stray kitten my dog has been displaying behavior that was threatening to me. Gradually over the past few weeks his warnings have become more serious and today he bit my hand this is the first time he's ever done this to me. I feel like this cat my daughter brought in the house has a lot to do with it since his behavior changed over night once the cat came in. I've had my dog ever since he was a puppy he is 2 now and he is not neutered. I don't know if that has anything to do with it. He is only biting or threatening to bite when you grab his collar or try to handle him in that area so I assume he feels threatened for some reason and he's reacting to that. But why all the sudden? He's always been such a good dog and a real sweetheart. I'm so upset about this. What do I do to stop this new bad habit of his? Does this have anything to do with the cat? Do you think that he feels he's trying to prove that he is alpha, or is he getting territorial and he's trying to display dominance?