I'd never heard of Friction Mallets until a guy from a New York City recording studio asked me to make some. He described their design. I built a bunch of prototypes so I could see what worked and what didn't.

Essentially a friction mallet is a length of cable with a superball on each end. (...I bet you wish that YOU had thought of that!) When you hold it in your hand and let the two balls drag across a smooth surface the balls vibrate making some very wild sounds. They can sound like whales, a race car, a cello, not to mention some embarassing 'poop' noises! The ones with 2 different sized balls can produce a chord! Drag one across a door, a window, a drum(!!!), a wall, a file cabinet, the side of your car!

Friction mallets are ridiculous...and hard to put down. Only 8 bucks plus shipping.