The way I'd shoot him, he wouldn't feel nothing. I'd put the gun right there. Right back of the head. He wouldn't even quiver.
In chapter 1, Lennie asks George to tell him "about the rabbits". This is referring to their big dream of owning a ranch, nice house, and having all basic needs to themselves. George's abrupt interruption in the middle of telling his story indicates that deep down, it kills him to tell Lennie their dream, because he knows that it will never come true. This scene supports, as well as foreshadows, the reoccurring theme of dreams not coming true.
Chapter 4 Pages 72-73
Books ain't no good. A guy needs somebody-- to be near him. A guy goes nuts if he ain't got nobody. Don't make no difference who the guy is, long's he's with you. I tell ya, I tell ya a guy gets too lonely an' he gets sick.
In Chapter 2, Curley's wife comes into the bunk house, apparently looking for Curley. George sees that she isn't looking for Curley, but just the opposite; she was looking for trouble with other men. Her body language, flirty attitude, and the fact that Lennie can't keep his eyes off of her all suggest that she is going to cause some trouble for Lennie later in the story. This shows that Lennie needs to be careful, and has hopefully learned from past mistakes.
Chapter 5 Pages 90-91
I done a bad thing. I done another bad thing.
In chapter 3, Carlson shoots Candy's dog in the back of the head. Likewise, this scene foreshadows one later in the book, where another character is also shot in the back of the head. This event supports the theme of doing what is best for an individual is not always easy.
Chapter 6 Pages 105-107
I thought you was mad at me, George.
No. No, Lennie. I ain't mad. I ain't never been mad, an' I ain't now. That's a thing I want ya to know.
In chapter 4, Lennie goes into Crook's room and begins talking to him. Crooks, realizing that Lennie doesn't understand a word he's saying, begins telling Lennie about his life- all the good memories, and the hardships he goes through. This part of the scene is particualy significant, because it applies not only to Crooks, but also to Lennie. Lennie has always been an outcast, even as a child. The theme of this scene is a lonely man is no good for himself.
In chapter 5, Lennie accidentally kills his puppy by playing too rough with it. Not soon afterward, Lennie kills Curley's wife by snapping her neck. This scene shows how incredibly dangerous Lennie can be, as well as how clueless he is. Lennie's mistakes provide the importance of learning from your mistakes, and the dreadful consequences that can appear when you do not.
At the end of chapter 6, George shoots Lennie in the back of the head, just as Charlson had once shot Candy's old dog. Both of these shootings represent a turning point in a different character's life. For George, it was getting rid of the thing that stopped him from succeeding in his dreams, and had caused him so many problems. This last scene shows that sometimes, you have to do the wrong thing to do what is really right.