Professional version for the scene (large size)!

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You show the audience two curved shapes (arcs) of the same size: one red, the other yellow.

Place them next to each other.

What happened?...

The red arc has become longer, the yellow has become shorter!

Now swap the positions of two curved shapes.

Now yellow has become longer and red has become shorter.

Miracles and more!

A wonderful scientific experiment studying the illusion of size.