Dowsing

Dowsing, also known as water witching, is the practice of using a stick or some similar object to locate things hidden underground, like water, oil, buried treasure, even bodies. Several methods are used by dowsers in order to accomplish this. There are map dowsers, who hold a pendulum over a map to locate the desired object . Then there is the original method, called field dowsing, where the dowser simply walks around holding a dowsing rod and follow the direction in which the rod points. People who practice dowsing claim to have a special power enabling them to sense the energy, in the form of vibrations, of an underground object. In order to feel these vibrations they need to be holding a stick or rod of some type. Now how does this work? If you were to ask this, even experienced dowsers don't have an answer. They simply say it is a power they possess that enables them to find the hidden object. There is no science that backs up the legitimacy of dowsing, This along with the fact that even those who practice dowsing can't explain how it works leads to the conclusion that it simply doesn't happen. There just isn't enough evidence showing it's validity.

http://paranormal.about.com/od/dowsing/a/All-About-Dowsing.htm

http://www.skepdic.com/dowsing.html