Lennie is like a child in his thinking. The game he plays here with George is the classic "If I have my hand over my eyes, no one can see me," thing. This kind of sleight of hand is the unique stuff of childish thinking.
Crooks goes back to a place of innocence in order to find his sense of belonging. The way that others have hopes and dreams of a future, life has dealt Crooks a raw enough hand that his only way to have happy thoughts is to recede back into this memory. When the other guys talk about their dream farm, Crooks has difficulty doing anything but beating their hopes back. Likely, the world only seemed good when he was free of understanding prejudice and hardship. After losing that freedom, it’s no surprise Crooks sees things in such a harsh light. Crooks has replaced his dreams for the future with bittersweet memories of the past.
Freedom and confinement
George is sure to be a hard worker, but it’s clearly not the thing he enjoys best. For George, as for most people, it’s nicer to enjoy the woods than to be busy "bustin’ a gut" at work. Although George doesn’t have the same simple delight in nature that Lennie does, what he really revels in is the freedom from work, the chance to spend a lazy evening under the stars. It almost seems that there’s a reason George has been a traveling man of the road, rather than getting tied down to any one place. Transient living has its downsides (like poverty and homelessness), but being free is priceless.
George’s outburst concludes with a wish that he could lock Lennie up (presumably trapping him the same way George feels confined by their friendship). Once he’s said this awful thing, he stops himself from ranting and becomes ashamed, especially once he’s seen how he’s hurting his friend. This is an important moment of distinction between confinement that’s forced on you and confinement you choose. Friendship shouldn’t be a kind of prison, but rather a voluntary bond. George knows the difference.
George doesn’t kill Lennie out of anger, but he doesn’t seem to do it out of justice, either. It seems that George has no choice but to kill Lennie. The same way George has protected and guided Lennie throughout life, he now leads him into death. George is confined by choice, and Lennie is freed by death.
Justice
George knows even before they go to the new ranch that Lennie is bound to get into some trouble. He even says it’s a foregone conclusion, as it’s what Lennie has always done before. We get an insight into George’s sense of justice here: no matter what Lennie does, George is willing to meet in the brush and presumably run off again with him, just like they left Weed. George seems to think that together, they can keep getting out of whatever scrapes Lennie gets into, rather than stick around and wait for justice to be served. Given what happens at the end of the book, George’s statement here makes us wonder whether his views on justice change over the course of the book.
George has already noted that if Lennie fights with Curley, both George and Lennie will lose their jobs. Still, in spite of this practical reality, George has a sense of honor and justice that is worth more than the job. If Curley hits Lennie, there’d be more to lose by backing down than what would be lost by winning the fight – or so George’s sense of justice tells him.
There’s some strange justice afoot here. Clearly, Curley got what was coming to him, and if Slim says Lennie’s all right, then Lennie’s all right. Still, it’s noteworthy that Slim doesn’t outright admonish Curley for doing a bad thing. Instead, Slim threatens to "tell ever’body" something such that Curley will be made a mockery. Perhaps for his losing the fight with Curley, or the looseness of his woman, Curley knows he’s in no position to argue. Justice has been served, but it seems no lesson has been learned.
Weakness
Lennie doesn’t seem to regard his mental weakness as a point of despair. Instead, he seems relieved that George is there to have his back. Lennie’s weakness might be responsible for the strength of his bond with George.
Lennie’s condition, or maybe his sentimentality, allow him to cry over his lost mouse. This might be mental weakness, but what’s particularly odd about it is seeing a grown man cry. Regardless, what’s most interesting about this bit is how George is considerably softened up by Lennie’s tears. He’s quick to point out he didn’t mean any harm – George has a weak spot for Lennie’s tears. If George seemed tough a minute ago, he makes it clear here that he’s actually a guy with a heart of gold.
Candy is too weak to defend his dog, even though he clearly wants to do so. Slim won’t give him any support, and Candy isn’t strong enough to just tell Carlson to get lost. The dog is old and weak, and though Candy initially seemed like its protector, we find here that he may not be so different from his pet after all. This is especially interesting when we consider, again, the parallels between Candy’s friendship with the dog and George’s friendship with Lennie.
Candy’s power comes in the form of the $300 he received as compensation for the accident he suffered on the ranch. His weakness is that, regardless of the money, he is now missing a hand, which keeps him from being able to work well. Candy understands that he’ll soon be useless to himself and others.
Lennie’s hallucinations seem to fully reflect Lennie’s real weaknesses and fears. Aunt Clara talks about how Lennie would never run away because he’s dependent on George. The big scary rabbit preys on Lennie's fear Crooks brought up -- that George might outgrow Lennie and leave him. It makes the audience wonder whether Lennie has, stored away in his consciousness, knowledge of what he’s done wrong and deeper knowledge of himself. Perhaps he just lacked the good sense to access it, and now that he has, something irreparable has happened. Lennie as we know him – slow, but mostly sane – might have lost some of his sanity after he killed Curley’s wife. Of course, there is no way to know for sure.