Radioactive Snakes From Mars

How does the game Radioactive Snakes From Mars work?

The objective of this game is to keep your snakes alive. So far it sounds easy, but the problem is that these snakes are radioactive and they need to eat constantly to stay alive. They can only eat radioactive pills and each of them will have a different effect on the snake, but they'll all make the serpents grow. When you've eaten all the pills on the level, you'll get to the next feeding area.