It's a free game that squashes the bad bacteria and multiplies the good bacteria with a continuous hit.
If you're not careful, bad bacteria will multiply in the blink of an eye and it will be game over, so you should keep hitting without resting.
It looks like a simple game, but you can feel the tension unexpectedly.
Greens are good bacteria, so don't crush them!
All but green are bad bacteria. Feel free to just keep hitting them and crushing them!