This is a simple but fascinating demonstration of Muscle Wire® material technology. It looks like a regular spring. Pull it out and it snaps back. It has superelastic properties, so you can pull it out a really long way and it will snap back.

If you pull it out a long way- enough so if it were a normal spring, it would be overstretched and permanently distorted, and hold it for about five seconds, it looks any spring would look if it had been overstretched. But this is a shape memory alloy, and we have set the transition temperature to a bit below body temperature. When you hold it in your hands, you warm it up and it goes back to normal.