I read about that phenomenon as a kid... An Archer (Radio Shack) project book claimed that the fillings in some peoples teeth formed a crystal radio.

Now, I'm 38 with a Ph.D. in physics and I've yet to figure out how saliva and mercury amalgum can mimic the characteristics of crystal/germanium diode. <img src="images/graemlins/crazy.gif" alt="" />

It's definitely a real, and apparently somewhat common, effect tho...