This remarkable one-minute experiment demonstrates the tremendous difficulties our brain has to enfold three-dimensional structures.
Use the pair of scissors along the red lines to cut off two long strips from the sheet of paper.
No - size does not matter! ☺
Use the glue stick on both strips of paper to build two identical paper "rings".
Mathematically spoken, each of these rings is the lateral surface wall of a right circular cylinder.
Place one ring on top of the other, rotate the upper ring 90° about the vertical axis and glue both rings together.
Now - before you actually do it - imagine to cut each ring along its red center line into halves. Yes - you are supposed to cut both rings all the way through, until they fall apart!
Can you imagine what you will hold in your hands? Will it be one ring or two or four? Will they be connected to each other, interlocked, or separated? Or will it be something totally unexpected ...?
Only very few people can actually twist their imagination to come up with the correct answer. If you are not one of them, just do the cut and you will definitely enjoy the astonishing picture!
Thanks to Gitti for this very nice little brain teaser ...