I guess it's a mouse with a ball on the underside..if so, a quarter turn to the left of the collar surrounding it will release the ball. Take it away and wash it. While it's out look inside, you'll see some really tiny rollers around the edge of where the ball sits. If you have pets or you're just plain dirty in general these rollers can get clogged up with all sorts of horrible stuff. Just joking, my wife is unbelievably house proud but it still used to happen to me before I went cordless and optical. Clean the rollers and reassemble. Should be fine!