Tap on a cell that can shoot to start a chain reaction. Observe the play area to identify which microbes are able to fire and which are not. Plan your clicks carefully to ensure each shot hits the target microbes. Prevent touching target cells as it will break the chain. Continue tapping active microbes in the right order to cleanse the field of all non-shooters. Complete each level by wiping out all non-shooters with the minimum taps possible.