The Möbius strip or Möbius band is a surface with only one side and only one boundary component. The Möbius strip has the mathematical property of being non-orientable. It is also a ruled surface. (check on wiki)
It has been used to explain complex, meaningful ideas such as time travel. But this simple, trivial music box, which uses a punch strip in the shape of a Möbius strip, might be my favorite application of the idea. It’s a familiar tune which can be played upside-down and backwards, and then just backwards, and then upside-down and backwards again. Over and over, forever.
View the video below to see how it works: