Georege kills Lennie because he killed the woman that was with him in the barn because she caught lennie trying to hide the dead pup which he accidently broke its neck because he patted it to hard and bit him, and lenny didn't know when to let go of the womens hair and she screamed so he panicked and broke her neck. Lennie ran away and George couldn't take care of him anymore so he had to kill Lennie.
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