The magician shows the audience a small black magic wand and a large cube.

In the middle of the cube there is a hole just big enough so that the wand can be pushed through it.
The magician does so, as shown in the diagram. What is this?

The wand is getting smaller and smaller and almost completely disappears into the cube!

Wait a minute, now its coming out of the other side of the cube, but it has changed COLOR!

Everything can be examined immediately!