Escher’s Ants and the Mobius Strip
A Mobius strip is a ONE-SIDED two dimensional object. Take a flat strip of paper and join the two ends after twisting one end 180 degrees. Now put the strip on a hard surface and trace a line on it with a pencil without lifting the pencil until your line meets up with the beginning of itself. This will prove that the object has only a single side. Escher’s ants, above, will walk on what looks like both sides of a two sided object, but watching one of them will reveal they manage to do this without ever leaving the surface of the strip, because it now has just ONE SURFACE.