The TechZone has reviewed the world's thinnest mouse.

And it doesn't get much more compact that the ridiculously skinny Slim Mouse from 2P. This mouse is so thin that it fits inside the PC slot on the side of your notebook. In this way, you don't even need to dedicate a pocket in your backpack or laptop bag for the mouse: it fits INSIDE your notebook.

2P Slim Mouse Laptop Mouse Review