Materials: coated cable, compressed synthetic rubber
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 one or both 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 more embarrassing noises! Dragging both 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 have become very popular to use on gongs. Paramount Pictures commissioned me to build a huge assortment of friction mallets to drag across gongs as a film soundtrack effect. Since that time, several gong masters of national prominence have made me their friction mallet supplier.
I'd never heard of Friction Mallets until 20+ years ago when a guy from a New York City recording studio described what he had in mind and asked me to make some. I built a bunch of prototypes so I could see what worked and what didn't. I even got feedback from gongists until I found which balls worked best on Paiste, Zildjian, and Wuhan gongs.
When I first started building these, decades ago, I was lucky to sell two per year. Today, playing gongs has become so popular, that I sell them weekly. There are drum stick manufacturers who began putting superballs on sticks and selling them for ridiculous prices several decades later. But superballs on cables vibrate much better than they do on hardwood sticks.