The fold
Use a paper bill or a strip of stiff paper about three times as long as it is wide. Hold it horizontally with both hands.
- Make an S. Fold the strip into thirds without creasing hard, so that viewed from above it forms an S (or Z). You now have three panels: a front panel, a middle panel, and a back panel.
- Clip the first pair. Slide one paper clip over the top edge so it grips the front panel and the middle panel together, and nothing else.
- Clip the second pair. Slide the second clip over the top edge so it grips the middle panel and the back panel together, and nothing else. The two clips should not overlap, and neither clip should hold all three layers.
- Pull with conviction. Take the two ends of the strip and pull them firmly and quickly apart, straightening the paper. The clips slide toward each other, pop off the top edge, and come off linked.
Why it works: The middle panel passes through both clips. As the strip straightens, each fold travels through its clip and pushes the clips together until they lose their grip on the paper, and each clip ends up hooked through the other.
Make it play
Ask someone to inspect the two clips first. Pull fast; a slow pull lets the clips slide off one at a time. With a bill, a little patter about money bringing people together lands well. With practice you can catch the linked clips in the air.
If they come off unlinked
Check that each clip holds exactly two layers, and that one clip is on the front pair and the other is on the back pair. Use standard-size clips; tiny ones tend to fall off before they link. Pull away from faces, because the clips really do jump.
Pair it
This is a natural opener for the jumping rubber band: both use objects from any desk drawer, and both can be handed out for inspection straight away.
Next: The magnetic pencil