An example of symbolism in Of Mice and Men is the puppy. The puppy symbolizes Lennie’s vulnerability.
Symbolism is something that stands for something other than itself. For example, the river in the beginning of the novel symbolizes life. Candy’s dog symbolizes his vulnerability, and Lennie’s puppy symbolizes his.
It is no coincidence that Candy’s dog is shot early in the novel. This foreshadows the difficulty Lennie will eventually face. The dog is vulnerable because it is old and no longer useful. Candy faces this same vulnerability at some point very soon.
Lennie is strong and child-like. Since he does not know his own strength, it sometimes gets him into trouble. He really likes soft things, like the puppy.
Lennie held out his hands pleadingly. "Give 'um to me, George. I'll take 'um back. I didn't mean no harm, George. Honest I didn't. I jus' wanted to pet 'um a little." (ch 3)
George’s concerns are well-founded. He knows that Lennie sometimes tries to pet things like mice and accidentally kills them because he is too strong. George lets him play with the puppy when it is older. Unfortunately, Lennie cannot stay away. The puppy is still too young, and the next thing we know he has petted the puppy too hard and killed it.
And Lennie said softly to the puppy, "Why do you got to get killed? You ain't so little as mice. I didn't bounce you hard." (ch 5)
Ironically, Lennie’s vulnerability is his great physical strength. It puts him in danger, because he accidentally kills Curley’s wife and George has to shoot him.
Just as Candy’s dog had to be shot to put it out of its misery, George has to shoot Lennie. He knows that Lennie will be arrested and will not understand what is happening to him. He will be miserable. George protects him by killing him.