Electric Border Collies: "For thousands of years, humans have been herding. Goats. Sheep. Cattle. It's not always easy, and modern ranchers usually have help. They use a Border Collie to keep their beasts together. These dogs are amazing; if they can see it, they can herd it. But what do you do if you want to herd, say, microbes?
"It's not as silly as it sounds. Onboard a spaceship, for instance, a few microbes floating in the ship's drinking supply could be a harbinger of trouble to come. The same is true of urban water supplies. What if terrorists dump pathogens into a city reservoir? Herding microbes together for testing and eradication could save the day."