What we have here is possibly the World’s smallest wireless mouse, the Lingo which measures in at a tiny 27.5 x 60 x 19mm and weighs in at a tiny 23.g.
As you can see from the photo the mouse is pretty small, it comes with an 800dpi resolution, and has a range of about 10m.
It runs of one AA battery which will give you about 15 hours of usage, unfortunately it is only available in Japan for around $50.