Mac Mouse

the wireless one is and the wired is optical... but just think lasers bounce off mirrors... Shiny surfaces will do the same. So it could "confuse" the mouse.

I could be wrong

It's not just shiny surfaces. In both laser and LED mice, the photosensitive component needs to be able to detect changes in the surface, if you are on a shiny or transparent surface then the change in the surface will either be too bright or there will be no surface that is changing if you are working on a glass table. The only time when analogue mice seem more useful .

I am using my mouse on a piece of paper and its working perfectly.