A metal can remember a shape

Nitinol, an alloy of nickel and titanium, can be bent while cool and returns to a trained shape when warmed through a phase change.

Nitinol has two solid phases, martensite when cool and austenite when warm. Deform the martensite and you are moving twin boundaries, not permanently scrambling the metal. Warm it through the transition and the austenite lattice reasserts the shape it was trained into. The training is a heat treatment. The remembering is a phase change.

The alloy was found at the Naval Ordnance Laboratory in the early 1960s, which is where the name comes from. It is used in stents that unfold at body temperature, in couplings, in actuators. It fatigues, it can be trained badly, and it is not magic. It is a repeatable rearrangement of atoms.