Plural mice mice or mouses A hand-held input device that is moved about on a flat surface to direct the cursor on a computer screen. It also has buttons for activating computer functions. The underside of a mechanical mouse contains a rubber-coated ball that rotates as the mouse is moved; optical sensors detect the motion and move the screen pointer correspondingly. An optical mouse is cordless and uses reflections from an LED to track the mouse's movement over a special reflective mat which is marked with a grid that acts as a frame of reference.