Lennie breathed hard. "You jus' let 'em try to get the rabbits. I'll break their God damn necks. I'll... I'll smash 'em with a stick." He subsided, grumbling to himself, threatening the future cats which might dare to disturb the future rabbits.
What is the significance of the above statement by Lennie when George tells Lennie he'll have to make sure their cats don't get the rabbits?