Because otherwise they would be unable to track movement and move the cursor in the computer screen.
There wasn't a hole in my dad's space-time continuum.
A hole in Juan
One is a group of cunning little runts.... the other is a group of running little C
Forty feet of track - all straight!
Mouse to Mouse resuscitation.
A. There is cheese in front of the mouse.
I'm having a movement"
Because your foot would go right through the computer screen!