When the big guy is trying to get away from Sam, ham, and company, he unexpectedly runs into a curious sight: Sam and a fox in a red box that's hanging from a (blue) tree. Whew.
Sam asks him, "Would you eat them/ in a box?/ Would you eat them/ with a fox?" (38-41). Do you recognize this box—do you? Does it give you déjà vu?
That's what too many late nights reading The Cat in the Hat will do to you. Yep, this looks a lot like the cat's big, red FUN-IN-A-BOX, the box that houses Thing One and Thing Two. Thing One and Thing Two, as we know, are symbols of pure, unadulterated, carefree mayhem. Sam and the fox become wacky doubles for Thing One and Thing Two, due to their (temporary) residence in the box.
On the next page, as we see the big guy angrily stomping down the hill away from the box, the box appears to be empty. When Thing One and Thing Two are released from the box in The Cat, the wild rumpusing begins in earnest. We're pretty sure the empty box in Green Eggs and Ham signals that the party is about to get started here, too.
Get ready to rumpus.