bumblebee-sized drones that kill cheaply using minimal explosive power by shooting people in the eye, which is soft enough to allow even a small projectile to continue into the brain. Or they might latch on to the head with metal claws and then penetrate the skull with a tiny shaped charge. If a million such killer drones can be dispatched from the back of a single truck, then one has a horrifying weapon of mass destruction of a whole new kind: one that can selectively kill only a prescribed category of people, leaving everybody and everything else unscathed.