The magician takes a quarter and an empty soda or beer bottle. The magician then causes the coin to penetrate the bottle. It looks completely impossible; the coin is really in the bottle. The bottle is completely examinable. And that's not the only thing you can do with this special coin.
Check out this performance as well:
You get the special coin and hours of magic video instruction—showing you dozens of effects that are possible with this (and other) gimmicked coins.