After hearing of the dream Candy wants to be included, mainly so that he would not be left alone. Crooks at first didn't believe Lennie but when Candy told him that the dream was to become a reality he also wanted to join them so that he wouldn't become alone.
The novel describes a society that has an aspect of racial prejudice. Steinbeck shows that Crooks is intelligent as he reads books and that he like everyone else needs warmth and companionship. But being black in those times denied a man of these common qualities. This brings out a dark side to Crooks, on that enjoys the torture of someone who doesn't deserve it.
As well as many themes the novel also has quite a bit of symbolism. The death of Candy's dog is one form of symbolism in the novel. The killing of the dog was a mercy killing, for the dog's "own good". It was shot in the back of the head so that it wouldn't feel any pain. The killing of Lennie was exactly the same. George shot Lennie out of mercy, so that the brain-damaged giant wouldn't be put in to prison. Also George wanted Lennie to die happily, he told Lennie to turn around as well as telling him that they were about to carry out "the dream". He shot Lennie in the back of his head, a painless end, just as Candy's dog had been killed by Carlson. Also George wanted to shoot Lennie himself and didn't want him to be shot by Curley. This is because Candy, after his dog had been killed, had showed regret that it had been Carlson who had killed his dog and not himself. George wanted it to be on friendly terms.
Another sign of symbolism that John Steinbeck gives us in this novel is when Lennie has just killed Curley's wife. "A pigeon flew in through the open hay door and circled and flew out again." I think that this simple sentence consists of religious meaning as well as traces of morality. One of the first things I noticed about this sentence is that a pigeon is the same variety of bird as a dove and doves are a sign of piece and harmony, which blends well with the death of Curley's wife.
