Tenyo is a Japanese magic trick company that's been around since 1960. They are well known for making clever props. (My friend Richard Kaufman, who often writes for Boing Boing, wrote a 1,400-page two-volume set about the company, called Tenyoism)
Here's a Tenyo puzzle trick called The Perpetual Puzzle (It's available on Amazon). You start by showing a rectangle made from 5 pieces. The rectangle fits snugly in a black plastic frame. Next, you show a sixth piece and combine it to the other five to make a larger rectangle. This rectangle also fits perfectly inside the frame. Finally, you show an even larger seventh piece, add it to the other six to form a rectangle. It, too, fits into the frame. How is it done? (If you know, please don't reveal the secret in the comments.)
