Outside In

> 19. Given a solid ball in 3‑dimensional space, there exists a decomposition of the ball into a finite number of disjoint subsets, which can then be put back together in a different way to yield two identical copies of the original ball. While you're at it, you can completely turn that sphere inside out without creating any holes or creases[1]. [1] [VIDEO]

Here are two classic youtube videos on the topic of sphere eversion; they mostly overlap, but I am posting both for double the hilarity in the comment sections :) (the full 21 minute one) [VIDEO] (the first 10 minutes) [LINK] If I remember correctly, I think the 10 minute one has the more hilarious comment section.

Sort of a tangent, but here's a 20m video explaining how to invert a sphere without tearing it: [VIDEO]