### Paper, Scissors, Imagination

This remarkable one-minute experiment demonstrates the tremendous difficulties
our brain has to enfold three-dimensional structures.

#### What you need

- Sheet of paper
- Pair of scisssors
- Glue stick

#### What you do

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 ...