"I was only foolin', George. I don't want no ketchup. I wouldn't eat no ketchup if it was right here beside me."
"If you don' want me I can g off in the hills an' find a cave. I can go away any time."
"I don' like this place, George. This ain't no good place. I wanna get outa here."
"I’d pet ‘em, and pretty soon they bit my fingers and I pinched their heads a little and then they was dead—because they was so little. I wish’t we’d get the rabbits pretty soon, George. They ain’t so little."
just some key ones:
the first one shows he cares for george
the second one shows he can tease george and he has childlike behaviour
the third one foreshadows trouble
the last one is foreshadowing that Lennies gonna kill more things