Eye popper

It consists of a small, dome-shaped piece of rubber or similar material resembling a half of a rubber ball; the shape of a smile is often imprinted on the dome.

When pressed, the object inverts and becomes unstable and, after a few seconds, undergoes snap-through buckling to pop back into its original shape, making a loud popping sound.

[1][2][3] If resting on the ground when this happens, the toy will fly several feet into the air.

It can also be thrown on the ground, causing it to pop upward.

[3] The eye popper's behavior resembles the process by which a ball compresses upon hitting a hard surface.