Why does your macintosh mouse jump around randomly?

Answer

Sometimes this can occur, with an optical mouse or a mechanical mouse (with a ball in it), if it's sitting just right; basically the wheel that detects movement in the mouse is sitting right where it would appear to be moving, and makes the mouse sensitive to vibration. An optical mouse doesn't have a wheel, of course, but its image sensor can get confused when it "sees" just the right image of the pad or table. Move the mouse ever so slightly and see if the random movement stops.

If the mouse behaves erratically consistently, especially while you're using it, then the mouse itself is probably damaged.

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