When i once went caving, the guide got us to turn off all our helmet lights and told us he would do a cool trick with a polo he had in his hand. When it was pitch black (no light from the surface or anything) he snapped it and a very small white spark/flash appeared for a second. How the hell does that work?!
I have heard a similar story with a sweet called Lifesavers (like fruity polo's but American). I'm not sure what causes it but I'm sure they investigated the story on www.snopes.com :)