For $25 dollars and 2500 hours of practice you TOO can perform this trick. Check out...
http://magicshop.magictricks.com/Expanded-Coin-Shell-Half-Dollar_p_171.htmlFrom the ad:
The expanded shell is a shell that is slightly larger than a half dollar, and is made to fit over the half dollar (thus, for example, making it look like you have two coins in your hand, and when the shell fits over the half, now you only have one).
Did I ruin it? My Uncle used to do a bit of that stuff. The real trick is learning how to be that damn smoothe with your hands.