A Chinese finger trap (also known as a Chinese finger puzzle, Chinese thumb cuff, Chinese handcuffs, and similar variants) is a gag toy used to play a practical joke on unsuspecting children and adults. The finger trap is a simple puzzle that traps the victim's fingers (often the index fingers) in both ends of a small cylinder woven from bamboo. The initial reaction of the victim is often to pull their fingers outward, but this only tightens the trap. The way to escape the trap is to push the ends toward the middle, which enlarges the openings and frees the fingers. The single-ended version, sold as a "girlfriend trap", has been available since at least 1870, when it was recorded as a "Mädchenfänger" or "girl catcher". Design The tightening is simply a normal behavior of a cylindrical, helically wound braid, usually the common biaxial braid. Pulling the entire braid lengthens and narrows it. The length is gained by reducing the angle between the warp and weft threads at their crossing points, but this reduces the radial distance between opposing sides and hence the overall circumference. The more one pulls, the more the circumference shrinks and the trap tightens. The same effect is used in specialized textile manufacturing, the Vivien Kellems cable grip, Indonesian woven fruit presses, and by fly-fishers. Chinese finger traps are not intended for use as restraint devices. Victims of the prank may break the bamboo strips through physical strength when they pull outwards, attempting to free their fingers and stretching the trap beyond its limits. Variants One variation on the Chinese finger trap has uses in orthopedic medicine—namely, providing even pressure to the patient's digit(s) and at the same time immobilizing the joints—and serves a similar purpose as a traction device. Its development goes back to Austria in 1870 when Dr. Steinberger, a dentist at the Rudolfsspital in Vienna, reported the discovery of his doctoral student Schmall, who got the idea to use the toy ″Mädchenfänger" (girl catcher) for the extension of fingers and arms. The principle was adapted for the use in surgery, and already in 1873 termed "Schmall'sches Extensionsgeflecht". Another variant is the towing sock. It uses the same principle to seize the end of a cable to be pulled through a tube or tunnel. Cultural influence The Chinese finger trap is a common metaphor for a problem that can be overcome by relaxing, i.e.