This is a fairly old trick, but still a good one. If someone bet you they could cut a hole in a 3 inch x 5 inch index card (7.6 cm x 12.7 cm) and climb through it, you'd might think they were a bit nuts. But beware if they happen to be a mathematician with knowledge of topology. As science educator Robert Krampf demonstrates in the this video.

It's not everyday you get to see someone make topology look like so much fun. But I found a few more fun tricks and puzzles involving topology, for example: 'stringing the ring', 'snip and clip', and 'the perplexing pencil puzzle'.

Will Knight, Tech editor

Labels: mathematics