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.
Those balls were nasty as fuck. I remember when I was like 13 and the mouse at my dad’s pc wasn’t working right. A friend recommended cleaning the ball…it was disgusting.