It is a motion sensor so move any part of your body to get rid of the splats on your screen (Full screen recommended). Hover over play and Score to either play the game or see the high score.
Thanks to Carol Vorderman's book with the original 'Window Cleaner'. Can you beat my high score? Type what score you get in the comments! Please do not use turbo mode on this game it is meant to be a fun game.