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."
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.
Hexaflexagons (Thanks, Fipi Lele!)