Electric forces.

The same thing happens when you push two magnetic north poles together, they spring apart again when you let them go, or when you lift a weight above the ground, it "springs" back downwards under gravity when you let go. The "information" of the molecules, as you call it, is simply the place where they have a state of equilibrium, where the net forces acting on them are equal in all directions, as they were before you changed their position by deforming the material.

In this case, though, the forces at work are electric.