Dunno what made me think of this just now. When I worked for IT in a school district way back in the 90s, a librarian told me she kept a supply of mouse balls in her desk because kids would steal them out of the school computers. What I remember about those balls was they picked up dust and crud off surfaces. Pretty soon optical mice came along and they were history.
By the time I hit grade school the balls were outdated. So I missed out on this. What I didnt miss out on was finding a broken (exposed) usb stick and when I would plug it into a computer it would shock me a bit and the computer would shut down. I felt like I had the ultimate power in my hands