There are three levels of play: Slug (slow), Worm (medium) and for those with the nimblest fingers, Python (fast).
Your task is to guide the snake so it eats the food. The quicker you eat, the more you score. And just like real food-eating snakes, the more you gobble, the longer you become. Try to steer clear of your own growing tail and avoid the walls... it won't be long before it's game over.