Buck finds puzzling the gratuitous cruelty of the adult men who have captured and caged him as he wonders what they want of him: "He could not understand what it all meant."
Buck is baffled about why these strange adults keep him in a cage and mistreat him so cruelly by not feeding him and not giving him water. And, to add to his confusion and puzzlement, some men leave him unharmed, such as the salon-keeper who merely opens the door to check on him by the dim light of a candle.
Further, Buck's feeling of puzzlement and oppression overwhelms him with a nebulous sense of danger and of misfortune that could come at any time, because whenever he hears the shed door rattle and he hopes to see the Judge or his men, there appear only other strange adult men, adults who puzzlingly torment him for no apparent reason.
The Call of the Wild by Jack London is considered by literary critics to be this author's perfect work. For, its naturalistic theme certainly plays well in the setting of the prospecting Klondike of 1897 in which man and dog, both creatures of an indifferent universe, confront a brutal environment that tests their survival instincts and strength.