It's funny and adorable the way cats can contort themselves in all sorts of weird positions and be comfortable.
Their love affair with boxes is also fascinating. Apparently all sorts of felines share that affection for boxes. It's not just house cats.
Indeed the positions a cat can sleep in are just plain weird. Twisted while lying on a rear leg with a paw in front of the eyes and the tail as a blanket draped over her.... that was the position I went to get my camera.
And I have seen some lions play with a card box at a zoo once now that you mentioned it. Same sight as if your cat at home was playing with a "tiny" box.