Jumping disc novelty – silver on one side, gold on the other

When you indent a disc and place it on a flat surface, after a while it will spring back into its original position and jump several feet into the air. Advice on how best to make it jump may be found here. On the gold coloured side, these discs have a circular indent close to the circumference. This feature is not present on item N2554 which otherwise appears to be identical.