If you have a computer with a male mouse (a mouse with a ball underneath), dust or crumbs inside it can prevent the ball from rolling smoothly. Most mice with balls have a way to remove the ball for cleaning, usually by turning a plastic ring that surrounds the opening for the ball or by sliding the ring to the front or side. (We don’t begin to suggest appropriate names for that ring.) Turn the mouse over so that the ball falls into your hand and not on the floor, gently wipe off the grit, carefully pick the lint off the little rollers inside, and snap it all back together. Female mice (optical mice, with no balls) appreciate it if you occasionally wipe off the mouse pad with a tissue. Also, look at the bottom of your female mouse: If it’s turned on and working, you see a little red LED through one of the openings.