*All quotes are taken from the Penguin edition of "Of Mice and Men" (1993)
Lennie is telling Curley's wife about the rabbits he and George are going to get. Lennie likes to touch soft things. Curley's wife is compelled by Lennie's childish nature: " 'You're nuts,' she said. 'But you're a kinda nice fella. Jus' like a big baby. But a person can see kinda what you mean. When I'm doin' my hair sometimes I jus' set an' stroke it 'cause it's so soft.'" (Pg. 90)
She lets Lennie touch her hair to see what it feels like, but Lennie gets carried away. She tells him that he will mess it up, but he continutes to stroke her hair. Finally, she starts to get upset, and starts to yell. Lennie doesn't like yelling, so he puts his hand over her mouth:
" 'I don't want you to yell. You gonna get me in trouble jus' like George says you will. Now don't you do that.' And she continued to struggle, and her eyes were wild with terror. He shook her then, and he was angry with her. 'Don't you go yellin',' he said, and he shook her; and her body flopped like a fish. And then she was still, for Lennie broke her neck." (Pg. 91)
George knew that Lennie didn't intentionally kill Curley's wife; George also knew that Curley would have Lennie killed--Lennie was misunderstood. George took Lennie down to the lake, and had him think about the rabbits and the ranch--Lennie was thinking about things that made him happy. George killed Lennie to save him from a society that misunderstood him.