There is much discussion of love, and more specifically, the love between dog and owner. Buck feels more for Thornton than he ever has for a human before – including when he was leading the good life back in sunny California.
He shows his love by biting Thornton gently.
Remember Buck’s feelings of transience? Well he does, too, and he is afraid Thornton will leave him. He therefore refuses to let the man out of his sight.
Buck is still feeling the primitive vibes. You can take the dog out of the wild but you can’t take the wild out of the dog.
He starts hearing this same "call from the wild;" he has this yearning to go live in the woods and hunt and howl.
To demonstrate how loyal Buck is, Thornton tells him to jump off a cliff. Buck starts to do it, but Thornton pulls him back. It was the least he could do.
Thornton gets in the middle of a bar fight and Buck gets viciously protective.
Buck saves Thornton from near drowning. This scene is heroic and dramatic and definitely worth a good read.
Seems like Buck has gotten a reputation for being awesome. Some men bet Thornton that Buck can’t pull a thousand-pound load. Thornton bets with money he doesn’t have. Fortunately for him, Buck pulls through and wins his master a ton of money.
Now everyone wants to own Buck, and they offer Thornton obscene amounts of money for him, which Thornton refuses with such words as "go to hell."