Two different colored ball pair appears at the center. You can expect any of the balls to come randomly and regularly from top or bottom. Your duty is to make the central ball-pair to match with the dropping balls. Just click on the central ball-pair to turn it up or downside. If the randomly coming balls are already matching to the central ball... then control your reflex; don't click! If you aren't fast enough to act on right time, you fail! Try again, you won't get bored!