Above are sixteen pairs of 'cards', shuffled. At first you can only see their backs. Click on any two cards and they will be turned over to reveal images of the Moon. If they show the same image they will stay face up, otherwise after a brief pause they will be turned face down again. The game is over when all the cards have been matched and remain face up.
You aim is to match all the cards in as few tries as you can. Thirty tries or less is extremely good, and any score less than forty counts as a "win".