This is a really fun and different effect that presented in the right context, will be a gem in your collection. It's wonderfully well-calculated and a trick that will make even your wisest spectators sleepless. Second-hand version in fine condition.
You open a nice wooden box and show that it contains some puzzle pieces that together form a perfect rectangle that accurately fills the box (12 x 14 cm.). You put the pieces on the table, assemble them again and say that with the puzzle followed an extra piece that you now take up from your pocket. You move the puzzles around a little and a moment after, you once again have a perfect rectangle - now with the new piece included! Fascinating...
You then take another piece up from your pocket. This slightly larger than the previous one. Once again you move around the pieces and you succeed in a moment, re-assembling it into a perfect rectangle! As a climax, you can put the puzzle back in the box. It's mysteriously not gotten bigger than before and still fits exactly.
You receive:
A beautiful box for storage.
The magic puzzle made of wood.
The frame of wood that you put the jigsaw puzzle inside - for a start and at the end.
Detailed and illustrated instructions.