The octopus is well known for its ability to slip into or out of tight places. It’s not so hard to do, when you don’t have a skeleton.
Cats do have skeletons, or so I’ve heard. Otherwise they’d wind up folded in your wallet or seeping outside under the closed door. Watch the one cat in this video practically pour himself into a glass jar that you’re sure is just too small to hold him.
Why do they do it? Free tin-foil hat to whoever knows.