More ideas from Yyk
That there is the Klein Bottle, first conceived of in 1882 by German mathematician Felix Klein. Klein's "non-orientable surface," as it's called in the math community, is like a Möbius strip in that you cannot distinguish inside from outside;

Klein bottle If you want to give a mathematician something to try to wrap their head around, a Klein bottle is a good place to start. A real Klein bottle is an object with no inside and no outside.