The most organic oscillator in the world

If you go into most pet stores, you can find a little fish called a Gnathonemus Petersii - a member of the Mormyrid family.

The interesting thing about this fascinating little animal is that it emits pulses of electricity into the water. It uses these tiny little shocks to locate food, other fish, and potential mates. You can actually listen to this electric fish rather easily if if use a small piezoelectric earphone or amplified speaker.
Because the fish uses the electrical signals to ’see’, the more it moves around the more signals it will produce.

Here’s an example of the assembled ‘oscillator’, done by the crazy kids at sci-toys.com: