Nitinol Shape Memory Paper Clip
Nitinol. It's kind of like Rain Main. Has an infallible memory and a habitual state to which it always returns precisely and without fail, but...it doesn't deal with deviations from what it knows very well. Also, it is an excellent driver.
A metal alloy sometimes referred to as "memory metal" or, more appropriately, Shape Memory Alloy, Nitinol is perhaps most famously used in the hilarious "bending teaspoon" trick. You know, give someone a teaspoon for stirring their coffee or eating their soup, and the second it hits the hot liquid it collapses like an old flaccid, uh...heat-reactive metal alloy. Sold here as paper clips, Nitinol's shape memory allows curious kids to bend, kink, spiral, and warp the wire as much as they want, and then watch it return to its perfect, original form when dunked in a dish of water heated to about 113 degrees F.
Made from Nickel and Titanium, Nitinol demonstrates two distinct types of crystal structure, depending on whether it is above or below its critical transformation temperature. Below that temperature--between about 104 and 115 degrees F in this case--Nitinol wire is completely malleable. But once the heat rises, its memory kicks in, and it snaps back to the state in which it was originally "cured".
Programming, or annealing, a piece of Nitinol requires holding it in its desired shape while the alloy is heated to and held for a period of time at a very high temperature--750 to 900 degrees F or so. Once it cools, the bendability properties set in, but the memory remains and snaps to any time the structure encounters even much milder heat levels thereafter.
In addition to Nitinol paper clips, vendor Grand Illusions also peddles a few other shape memory alloy wares, including a wire bent to read "Hot" and a spool of Nitinol for users to manipulate however they desire (beware, though, making your own shape takes some skill and proper equipment).