The answer to this question can be found in the chapter entitled "In Which I Learn to Season My Food." When Sam checks a trap that he laid to see if he has caught anything he can eat, he discovers that he has struck lucky, and there is an animal moving around in it. As he opens it carefully, a weasel shoots out before Sam can try to stop him. Note how the weasel responds to being caught in Sam's trap:
He popped up about five feet away and stood on his hind feet to lecture me again. I said, "Scat!" so he darted right to my knee, put his broad furry paws on my pants, and looked me in the face. I shall never forget the fear and wonder that I felt at the bravery of that weasel. He stood his ground and berated me. I could see by the flashing of his eyes and the curl of his lip that he was furious at me for trapping him. He couldn't talk, but I knew what he meant.
Thus Sam meets The Baron, which is the name that he gives to the weasel that lives very close to his tree. The Baron is distinguished above all else by his curious lack of fear in the presence of humans. The Baron, like other animals, becomes a kind of companion and friend to Sam during his self-imposed exile from humanity.