I've seen some people do that when they're using a usb laser mouse and the desk surface isn't that good.The laptop surface tends to make a decent mousemat in a pinch.
(
Mu Dinofiddler,
Tue 21 Jun 2011, 18:15,
archived)
I'm far more impressed with how they got that gorilla to use that computer.
(
Mu Dinofiddler,
Tue 21 Jun 2011, 18:15,
archived)