Chipmunk's Swimming Style

Okay, so listen up, you chucklehead. The joke is funny because it uses "nuts" in two ways. First, it means the chipmunk's actual nuts, like acorns. Second, it's a slang word for testicles. The chipmunk swims on its back to keep its "nuts" dry, get it? You probably don't, because you probably can't read a sentence like the average bear.