Q: Why did the chicken cross the Möbius band? A: To get to the other ... oh.
The Möbius band or strip, named after August Ferdinand Möbius, a nineteenth century German mathematician, is a well-known mathematical shape. It is a surface with only one side and one edge.

It is easily made by taking a paper strip and making one half twist before gluing the ends.

Take two Mobius bands and glue the edge of one to the edge of the other - you get a Klein bottle.