Lots and lots of them. Beats are programmed by putting the balls in receptor cups that represent different parts of a drum kit—kick, snare, hats, and (yes!) cowbell. It was designed by Peter Bennett, who’s working on his PhD thesis tentatively titled “Interaction-Design Techniques for Multimodal Musical Interfaces.” What any of this will mean for drum-machine design we have no idea. But maybe future drum techs will have to add “ball polishing” to their list of duties.