Candy and George are presented with the same dilemma in the course of the novel: the killing of a loyal companion. They have to make the decision that condemns a close friend to death.
Candy is forced to agree to the shooting of his dog who is very old and blind. The other men at the ranch complain about his smell and the fact that he isn’t good for anything any more. Candy holds out for a while, as he simply can’t bear losing his dog, who seems to have been his only real companion at the ranch. The kind-hearted Slim presents it as a case of mercy killing:
I wisht somebody’d shoot me if I get old an’ a cripple. (chapter 3)
This is no comfort at all for Candy. He knows he can’t prevail against the wishes of all the other men, however, so he finally turns the dog over to Carlson to be taken out and shot.
Candy later miserably remarks to George that he should have shot the dog himself:
I shouldn’t ought to have let no stranger shoot my dog. (chapter 3)
This foreshadows George’s mercy killing of his devoted friend Lennie after Lennie accidentally kills Curley's wife. George decides to shoot Lennie himself rather than turn him over to the lynch mob or to the authorities. It is a terrible thing to have to do, and his agitation clearly shows as he speaks ‘shakily’(chapter 6), his hand trembles and afterwards he just sits in silence.
George performs the act of killing Lennie out of compassion, which society would not have done. Like Candy’s dog, to society at large Lennie is a nuisance that has to be got rid of. However, George takes his cue from what Candy said earlier, that he should have shot his dog himself, and refuses to hand Lennie over to others. George allows Lennie to die happy, still looking out for their dream farm.