This is an optical illusion puzzler as well as a magic trick!
You start with a red envelope and a blue envelope.First, the red envelope fits inside the blue envelope.Nothing magical about that.But wait!Now the blue envelope fits inside the red one.What???!!How can that be??
It's a real mystery!
This one is very very easy too!It really works all by itself.If you can put one envelope inside another, you can do the trick!
And that's all you need!Envelopes are made of heavy paper.About 4.5" on a side.