Reading Time: 4 minutes There is a soldier lying on the ground, not fully dead. One zap and it stops moving. Job done. There, another soldier. And another. The battle has been messy, inefficient. Now the battlefield needs a clean-up. This is the role of a cleaner-upper. Another zap. There is a soldier still standing, suddenly behind, and it shoots, hits a leg before any cleaner-upper can prevent it. But there are seven more legs, and no falling ensues.