This is such a heart-wrenching chapter! Carlson illustrates the theme of intolerance; he embodies it the most in the novella. He is a white male who is strong physcially. Candy, on the other hand, has only one hand and is old, which is similar to his poor dog. Because of their distinct differences, Carlson represents those in society who only care for themselves. During this time period, there was no equality for a woman, the elderly, or a man other than a white man. Moreover, the dog is "cramping his style" so to speak. The dog stinks and is old, so Carlson does not think it has a purpose; therefore, he wants to just shoot it. He is a cold-hearted individual who lacks compassion for others.
In addition, this action also foreshadows the death of Lennie in chapter 6.
Not only does this scene show that Carlson is a callous man with no respect for Candy's bond with his dog, but it also shows how he views the elderly. Carlson is an example or ageism, discriminating based on age. He argues that Candy's dog is useless because it can't do any productive work any more. It just sits around smelling up the bunk house. Ironically, Candy is very similar to his dog. He can't perform very many usefull duties due to age and disability. He is only kept on out of a feeling of pity and duty. Carlson shows that he views nonproductive things as useless and disposable.
This heartbreaking scene lets us see what a callous man Carlson truly is. Candy has nothing save his dog. He is his only true friend and confidant. "I had him so long. Had him since he was a pup...he was the best damned sheep dog I ever seen," says Candy, defending his retention of the dog who was "no good."
But more than the loss of his companion, Candy sees how he will also be useless to the ranch very soon. He sees a horrific foreshadowing of his own fate, as Candy knows his best days are behind him. No matter how "good" he'd been in the past, he is only as good as his last "useful" day.