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.
Ha, these were early Macs (right at the launch of System 7) there was only a few kids with these at home so I had a pretty good idea who was brining in the icons and sound files (aiff if I recall correctly). We had one at my home too btw. They were interesting computers but besides shareware and a couple game companies, they were abysmal for games. We did get a copy of Warcraft 1 and could play it over 14.4k directly dialed to the other computer lines with PC users.