Dexter-
My dog's favorite thing is to grab a rope and be spun around. He will NOT let go, and if he breaks away from it, he will literally jump back up to catch the rope the second he hits the ground. He is obsessed, it is inbred into these dogs. That little dog was doing what comes naturally. He just needed someone to teach him that you do not do that to people. MY dog will play really rough, but the second my hand or clothing gets in his mouth, he backs right down. Of course, he is only 20 pounds, not 65-75 like a pit bull.