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The Pitbull seems to be the dominant one in the household as well the leader. When the friend tried to remove the puppy from the couch, the Pitbull saw it as a challenge to his first right to limited resources and his right to lead and control the environment and those in it, so he attacked the friend. When the owner separated the dog from the friend, the dog saw that as a challenge to his dominance/leadership role as well because she was trying to stop him from doing something and so then attacked her.
