A Chinese finger trap (also known as Chinese finger prison, Chinese finger cuffs, Chinese finger puzzle, Chinese handcuffs, Chinese finger torture and Mexican handcuffs) is a gag toy used to play a practical joke on children and unsuspecting adults. The finger trap is a simple puzzle that traps the victim's fingers (often the index fingers) in both ends of a small, woven bamboo cylinder. The initial reaction of the victim is to pull the fingers outward, but this only tightens the trap more.
The solution to escaping the trap is to push the ends inward toward the middle, which enlarges the openings and frees the fingers, before slowly twisting them out of the trap so as not to trigger the tightening reflex again. A second form of escape is to push one's fingers together and then grab the ends of the trap with one's middle fingers and thumbs. The fingers can then easily be pulled out.
There is nothing special about the bamboo or other material. The tightening is simply a normal behaviour of a cylindrical braid, usually the common biaxial braid. Pulling the braid lengthens and narrows it. The length is gained by reducing the angle between the warp and woof threads at their crossing points, but this reduces the distance between them and hence the circumference. The more one pulls the more the circumference shrinks (i.e. the trap tightens). The same effect is used in specialized textile manufacturing, and by fly-fishers
Chinese finger traps are not intended for use as restraint devices. Strong victims of the prank may break it when they pull outwards, attempting to free their fingers and stretching the trap beyond its limits. Any particular finger trap will eventually break due to repeated use.
The Chinese finger trap is also a commonly-used metaphor for a problem that can be overcome by not trying too hard to solve it, or a belief system that includes punishment for disbelief in itself.
The Chinese origins of this device are in dispute.