Lennie is thinking about how Aunt Clara would react to his situation. She's scolding him and reminding him to behave, to listen to George, and to think about someone other than himself. Aunt Clara is a figment of Lennie's immagination, he can imagine what she would say...... what George would say. His reaction to Aunt Clara is the same as it was in Chapter One when he had a similar conversation with George. He responds that he'll go off and live in the hills, so as not to be any trouble.
"Lennie moaned with grief. “I know, Aunt Clara, ma’am. I’ll go right off in the hills an’ I’ll fin’ a cave an’ I’ll live there so I won’t be no more trouble to George.”