When Carlson shoots Candy’s dog it is similar to George killing Lennie. Carlson wants to put Candy’s dog out of its misery because it stinks and is old and is of no use. In chapter 3 Carlson tells candy of how easy it would be to put the dog out of its misery. He tells him "Whyn't you get Candy to shoot his old dog and give him one of the pups to raise up? I can smell that dog a mile away. Got no teeth, damn near blind, can't eat. Candy feeds him milk. He can't chew nothing else.” Candy goes on to tell him “I’ve had him for so long.” Trying to defend the dogs existence. Carlson says “ well you aint bein kind leavin him alive.” Candy says “Maybe it’d hurt him.” Carlson replys “The way id shoot him he wont feel nothing.” Eventually Candy agrees and allows Carlson to take the dog outside to be shot. Thus putting the dog out of its misery.
In a sense it’s the same with George killing Lennie. Lennie is very slow and always gets himself into trouble. He isn’t able to do certain things without George he’s helpless like the dog and he’s unable to control it. Lennie’s speech is that of a young child. When George asks Lennie what would he want with a dead mouse Lennie replies “I could pet him while we walked along.” Or how he always wants to hear about the ranch “go on tell it George tell how its gonna be George.” Lennie is always causing trouble unintentionally and he like the dog is just there another useless tool.