Candy's Dog: "A dragfooted sheepdog, gray of muzzle, and with pale, blind old eyes" (26), Candy's dog is a far cry from his sheepherding days. Carlson says to Candy, in regard to the dog: "Got no teeth, he's all stiff with rheumatism. He ain't no good to you, Candy. An' he ain't no good to himself. Why'n't you shoot him, Candy?" (49). And Candy is left with no other option, but to shoot his longtime companion. This sub-plot is an obvious metaphor for what George must do to Lennie, who proves to be no good to George and no good to himself. Steinbeck re-emphasizes the significance of Candy's dog when Candy says to George that he wishes someone would shoot him when he's no longer any good. And when Carlson's gun goes off, Lennie is the only other man not inside the bunk house, Steinbeck having placed him outside with the dog, away from the other men, his gun shot saved for the novel's end.
The Cripples: Four of Steinbeck's characters are handicapped: Candy is missing a hand, Crooks has a crooked spine, Lennie is mentally slow, and Curley acquires a mangled hand in the course of the novel. They are physical manisfestations of one of the novel's major themes: the schemes of men go awry. Here, to re-iterate the point, Steinbeck has the actual bodies of his characters go awry. It is as if nature herself is often doomed to errors in her scheme. And whether they be caused at birth, or by a horse, or by another man, the physical deformities occur regardless of the handicapped person's will or desire to be otherwise, just as George and Lennie's dream goes wrong despite how much they want it to be fulfilled.
Solitaire: George is often in the habit of playing solitaire, a card game that requires only one person, while he is in the bunk house. He never asks Lennie to play cards with him because he knows that Lennie would be incapable of such a mental task. Solitaire, which means alone, is a metaphor for the loneliness of the characters in the novel, who have no one but themselves. It is also a metaphor for George's desire to be "solitaire," to be no longer burdened with Lennie's company, and his constant playing of the game foreshadows his eventual decision to become a solitary man.
The Dead Mouse and the Dead Puppy: These two soft, furry creatures that Lennie accidentally kills are both metaphors and foreshadowing devices. As metaphors, they serve as a physical representation of what will happen to George and Lennie's dream: they (Lennie in particular) will destroy it. Lennie never intends to kill the thing he loves, the soft things he wants more than anything, but they die on him nonetheless. The dead mouse is also an allusion to the novel's title, a reminder that dreams will go wrong, even the desire to pet a mouse. And because bad things come in threes, Lennie's two accidental killings of animals foreshadow the final killing of Curley's wife, an accident that seals his fate and ruins the dream for him, George, and Candy.