I want you to stop whatever you're doing right now and check your computer for holes. Specifically, one very long, very thin hole, or a door or tray that opens up and leads to same. If you find one, do not panic. It's called a CD-ROM drive, and — at least conceptually — there's something that you can do with it.
CD-ROM, as best as I can make out, refers to a technology that's been Comprehensively Depreciated - Radically OutModernized. Apparently, there used to be these fragile discs that held a limited amount of data that could be read very slowly and scratched easily. my parents had the same thing, and they were called records. We've moved on, but some computers still give over valuable space to various methods of reading these discs, space that you can now fill with something that's actually useful: a mouse.
I guess it would be more accurate for us to say that you could now fill your CD-ROM drive with with this foldable, flat-pack mouse if it was more than just a concept for the 2012 iF Design competition by designer Taewon Hwang, but it's clever enough that we're comfortable blowing some of our imagination juice on it. When unfolded, the mouse is flat and round and matches the size and shape of a CD, which means that you can store it inside your computer when you're not using it. When you need a mouse, just pop it out and fold it up, and you've got what looks to be a tolerably comfortable two-button mouse with touch buttons and a scroll wheel. Also, when folded it kind of reminds me of a 5.25" floppy. No, that's not a euphemism, kids. Get off my lawn.