You must prevent the ball from leaving the room. Three sides of the room have glass walls, and the bottom side is open — you can raise a glass wall at the bottom by tapping the screen or clicking the mouse button. Keep in mind that this wall only appears for a moment, so choose the right time so you don't lose the ball. The ball bounces around the room, and when it approaches the bottom, you must block its path. Be aware that the game gets harder and harder — the longer the ball stays in the room, the faster it moves.