Show the audience a hard steel ball. Put the ball into a brass box and press it inward with a solid brass block. The steel ball seems to lose its hard shell and becomes softer and softer, and finally it is pressed into a coin. All items can be handed over to the audience for inspection.【NOTE】Please prepare your own coin. The diameter of the coin is no more than 25.5mm and thickness is about 1.8mm, such as US Quater Dollar, Japanese 100 Yen.