Cut this loop down the middle and it refuses to become two loops
Take a strip of paper, give it a single half-twist, and tape the ends together to form a loop. Now run scissors all the way around the middle of the strip, cutting it lengthwise as if you're splitting it into two separate bands. Before you cut, guess: how many loops will you end up with?
Reveal the answer
One long loop, twice the length of the original, with two full twists in it — not two separate loops. The shape is a Möbius strip, first described in 1858 by August Möbius, and it has only one side and one edge, which is exactly why cutting it doesn't separate it the way it would an ordinary ring. Cut it again along its new middle and you'll get two interlocking loops, a fresh surprise every time.