Pearls!

The odds that an unopened Oyster contains a Pearl are approximately 1 in 12,000 (0.008%)

That's why pearl diving is like being in a garage band, sure it's a fun hobby but you're never gonna make enough money to feed yourself. But you can eat the oysters. Good advice dad.

(http://thelongestlistofthelongeststuffatthelongestdomainnameatlonglast.com/odds14.html)