In the Beginning of the book, it is kill or be killed. First, Buck goes two days and nights without eating or drinking while being transported north, foreshadowing his toughness. Buck witnesses curly die. For example, curly loses a fight with a husky and is brutally slaughtered by the encircled group of huskies eagerly watching the fight. Sense buck witnesses curly’s death he learns the law of fang. Dolly (who’s become rabid) attacks Buck who runs from her (although he has never seen a rabid dog before) until Francois clubs her in the head and kills her, saving Buck’s life.
In the middle, buck senses danger ahead, refuses to go on, John Thornton saves