In Of Mice and Men, how can the question Carlson asks at the very end of the story be answered?

In John Steinbeck's novella Of Mice and Men characters such as George, Slim, Crooks and Candy are portrayed as men of heightened sensibilities. They know that the world is not always a "black and white" place. They tend to understand that the world is a complicated place, often without clear moral conclusions.

At the end of the novel George is virtually forced into the mercy killing of his best friend Lennie, after the mentally challenged...

In John Steinbeck's novella Of Mice and Men characters such as George, Slim, Crooks and Candy are portrayed as men of heightened sensibilities. They know that the world is not always a "black and white" place. They tend to understand that the world is a complicated place, often without clear moral conclusions.

At the end of the novel George is virtually forced into the mercy killing of his best friend Lennie, after the mentally challenged man inadvertently kills Curley's wife. After performing the heartbreaking deed George is consoled by Slim, the leader of the working men on the ranch which is the setting of the book. Slim says, “You hadda, George. I swear you hadda. Come on with me.”

Slim's words are small consolation, but for George they let him know that at least one person realizes his love for Lennie and how he protected him and kept him free from abuse. If George had not killed Lennie the big man may have fallen prey to the brutality of Curley or the anonymous apathy of the legal system. At any rate, Lennie would not have understood what was happening to him if he had been captured. He only understood that he had done "another bad thing" and that George was going to "give him hell."

Unlike Slim, Carlson does not understand George's actions and in the very last lines of the novel he says, “Now what the hell ya suppose is eatin’ them two guys?” Earlier in the book Carlson shoots Candy's dog in what he calls an act of mercy, but in reality Carlson kills the dog because the dog is an irritant to him. Consequently, he does not understand that George has killed his friend for the very same reason that the old dog needed to be put down. 

Earlier in the book Candy confesses to George:

“I ought to of shot that dog myself, George. I shouldn’t ought to of let no stranger shoot my dog.”

George obviously took those words to heart and he denies Curley or Carlson the chance to kill Lennie. Both Curley and Carlson are static characters who cannot fathom the depth of affection which both George and Candy felt for their friends.