What did Buck do when he first heard the call of a wolf?

One night, he springs up from sleep with a start, hearing a call from the forest. He dashes through the woods and finds a timber wolf, one-third his size. Buck begins to circle the wolf and make friendly advances, but the wolf is afraid.

Finally, the two show their friendship by sniffing noses, and the wolf leads Buck away through the forest. They stop to drink, and Buck remembers John Thornton. The wolf encourages him to keep following, but Buck starts back toward the camp. When he arrives, Thornton is eating dinner, and Buck showers him with affection. For two days, he never allows Thornton out of his sight. Then, he hears the call more loudly than ever and is haunted by recollections of his wild friend. He begins to stay away from the camp for days at a time, hunting his own food.