Scot Nery sez, "Here's a quick fun video showing how to do the coin knuckle roll. Make your local magician respect and envy you."
How to roll a coin across your knuckles [TECHNICALITIES]
The incomparably great Vihart continues her Doodling in Math Class video series with a history and demonstration of the miraculous Hexaflexagon, a simple-to-fold paper hexagon that contains several iterations of itself, which can be found by turning it inside-out over and over again. Sure to delight, inform, entertain, and mystify!
Historical Note: This video is based on a true story. Arthur H. Stone really did invent the hexaflexagon after playing with the paper strips he'd cut off his too-wide British paper, and really did start a flexagon committee (which we'll hear more about in the next video). The details and dialogue, however, are my own invention.
(Thanks, Fipi Lele!)