A Chinese finger trap
A Chinese finger trap is a tube comprised of interwoven strips of bamboo. A finger is inserted into either end of the tube and when an attempt is made to remove them the tube only tightens, trapping the user's fingers. The trap is released only when both ends are pressed inward. The purpose of this device is purely humor oriented.
Data was puzzled by a Chinese finger trap during his briefing on the Tkon Empire, annoying Captain Jean-Luc Picard. Geordi later showed Data the solution to the puzzle. After an incident in the Delphi Ardu system, Picard allowed several boxes of the contraption to be beamed aboard the Ferengi vessel. (TNG: "The Last Outpost")