Ears are very handy for picking up sound -- but apparently, they make sound as well.
The noises are called "otoacoustic emissions", and everyone's inner ears make them. The noises are incredibly difficult to pick up though, and require powerful and sensitive microphones. One particular engineer at the University of Southampton, a UK resident named Stephen Beeby, is studying these ear-generated noises.
"Anecdotally, audiologists say they can tell different people apart - men, women, even people of different ethnic origins - by the profile of the widely varying types of emissions the clicks evoke," Mr. Beeby was quoted as saying. The sounds are unique enough, from person to person, that they have the potential of becoming a new method of biometric identification.
However, one drawback with using ear-noises as a biometric identification method is that over the course of a person's life, his ear-noises might change -- this is something Stephen Beeby is looking into. Also, if a person has been drinking or has an ear infection, the ear-noises might be affected.