The final chapter opens as Lennie waits in the bushes near the Salinas River, just as George told him to do in Chapter One. He nervously talks to himself, airing his worry that George won't let him tend the rabbits because of the bad things he did back at the ranch.
Lennie then hallucinates. He imagines the figure of his Aunt Clara - a plump, aproned woman with thick glasses - who scolds him for getting George into so much trouble. Lennie cries, begging Aunt Clara for forgiveness, and says that he will go off in the hills, where he can't bother George. Lennie then imagines a gigantic rabbit that mocks him for ever believing that he could tend the rabbits. The imaginary rabbit says that George will beat him with a stick when he arrives.
As Lennie sobs, George emerges from the brush. Lennie admits that he did a bad thing, but George appears not to care. Still upset, Lennie goads George into participating in their ritual routine of chastisement and forgiveness - he feeds George his lines about how much fun he would have if he didn't have to look after Lennie, and Lennie offers to go live in the hills and leave George alone. Lennie then requests the coup-de-grace: the story of how they're different from other workers and of how they'll have a farm together. George repeats these monologues woodenly.
He then tells Lennie to take off his hat as he continues to recount "how it will be" for them. He orders Lennie to kneel and pulls out Carlson's Luger. As the voices of the other men in the search party near their location, George tells Lennie one more time "about the rabbits," tells Lennie that they're going to get the farm right away, and shoots his companion in the back of the head.
Slim, Curley and Carlson arrive immediately after the shot is fired. Slim immediately interprets the scene accurately. Carlson and Curley, however, assume that George wrestled the Luger away from Lennie before shooting him. George, speaking in a whisper, affirms their false version of the events. The novel closes as Slim reassures George that he "had to do it," while Carlson and Curley look on in confusion, wondering why they are so upset.
Steinbeck's careful control of setting in the novel is especially clear in this chapter, which finds us back at the beginning - at the brush near the Salinas River. As he did in the opening chapter, Steinbeck begins with a description of nature. Once again, this nature vignette resonates with the themes of the novel. We see the casual violence of nature - the stork devouring the water snake - and we see Lennie's nonchalant integration into this atmosphere as he stoops and drinks with his lips like a thirsty dog.
The content of Lennie's thoughts, and of Lennie and George's eventual conversation, also mirrors the opening. Lennie repeats the child-like, ritualistic cycle of separation and reconciliation that has seemingly marked his relationship with George for years. Once again he hears George complain that he could live it up if not for Lennie; once again he offers to leave George and live in the hills; once again he gets George to tell him about their rabbit utopia.
However, these similarities - the setting and the content - only ultimately emphasize how much has changed since the novel's opening. Where George was once full of life - angry and forgiving - now he is a husk of himself, bereft of emotion as he goes through his monologues. What was once a plausible - if far-fetched - fantasy has disintegrated into delusion. He knows what must happen, even as Lennie goes on believing in the rabbits. Whereas in Chapter One we see George and Lennie's "best laid plans," here in Chapter Six we have irrefutable evidence that, just as Robert Burns' poem predicts, these plans have gone awry.
Emphasizing the delusional nature of Lennie's point-of-view, Steinbeck adapts his one experimental narrative gesture in the novel, choosing to depict two hallucinations - first Aunt Clara, and then (more ludicrous still) a giant sardonic rabbit. It is unclear whether we are supposed to understand these hallucinations to be one-time phenomena or regularly recurring. (By the way, the reader may find it a bit unbelievable that this gentle giant, who everywhere else proves incapable of understanding figurative language, is able to imaginatively generate such colorful self-chastisements as "you ain't worth a greased jack-pin to ram you into hell" (112).)
Either way, Chapter Six represents our closest approach to Lennie's experience - his simultaneous fear and love of authority figures, his relentless obsession with the rabbits, and his constant (if confused) regret that he never fails to act in a confused and problematic way. Lennie, social pack animal that he is, has a deep-seated need for discipline and forgiveness. His self-chastisement is quite moving, both because it reveals a degree of self-understanding in Lennie and because it suggests that he is regularly and brutally upset with himself. His remorse hardly counts as a conscience - at no point does he register that he has committed murder, only that he has done yet another inscrutable "bad thing" - but it makes a claim on the reader's sympathy nevertheless.
George's mercy killing of Lennie neatly parallels the events of Chapter Three, when Candy allowed Carlson to shoot his malodorous old dog. Steinbeck is even careful to involve the same Luger in each killing. Whereas the meek and passive Candy proved unable to do the job himself, George shows no such weakness. As has been proven beyond a reasonable doubt at this point, Lennie's lethal innocence is not compatible with the world. He cannot learn to change his ways - he cannot even understand why the "bad things" he has done are bad. The fate he would meet at Curley's (mutilated) hands - likely a drawn-out, vengeful lynching - is enough to convince George that his only real option is to make Lennie's death as quick and painless as possible.
At the novel's end, a few haunting questions remain. Why, after all, is George so attached to Lennie? What did he gain from the infantile and troublesome giant's companionship? Many theories have emerged over the years, as readers and critics have speculated that George is somehow specifically in Aunt Clara's debt, that George and Lennie are actually related after all, or even that George and Lennie are in love - romantically, not merely as friends. However, before (or at least alongside) such speculation, it's important to note that Steinbeck deliberately chooses to leave this central question murky. In a novel so carefully wrought in all other respects, this central motivational ambiguity stands as a deliberate and unsolvable mystery.
The simple answer may be that in the callous world of the itinerant laborer, the constant loyalty and companionship of a man like Lennie acts as an antidote to alienation. Lennie, paradoxically, represents the instinctual innocence in life. Writers as diverse as William Blake in his Songs of Innocence or Mark Twain in The Mysterious Stranger have explored the interesting ways in which innocence is not, in fact, altogether innocent. Divorced from a sense of good and evil, the truly innocent are capable of performing acts of apparent cruelty without remorse. Lennie is just such an innocent. He tempers George's worldly weariness with the constant presence of discovery and hope even as he plagues George's life with the threat of misunderstanding and ignorant folly. In many ways, Lennie completes George. And as his hollow despair at the close of the novel suggests, George ultimately needs Lennie's innocence just as much as Lennie depends on George's experience.