When Slim's dog has nine puppies, he drowns four of the smallest pups immediately because their mother cannot feed them. Slim tells Carlson that he kept the five biggest pups of the litter and ends up giving one of them to Lennie Small. Slim drowning the four runt pups is significant and develops Steinbeck's theme regarding the predatory, competitive nature of the world: the weak suffer and die, and only the strong survive. The runt pups are vulnerable beings and stand no chance of surviving in the dangerous, hostile world. Similar to the runt pups, who are drowned immediately after they are born, Lennie has no chance of surviving in the competitive, harsh world on his own. After accidentally killing Curley's wife, George is forced to humanely end Lennie's life, which is similar to how Slim kills the runt pups. The unfortunate runt pups symbolically represent weak individuals, who are taken advantage of and do not stand a chance of surviving the hostile environment.