Living in NYC with rats, I'm always reminded of Neal Stephenson's Baroque Cycle, where Jack Shaftoe is in Paris in the late 17th century and meets St-George, the city's preeminent rat-catcher. St-George explains how no one is never going to exterminate _all_ of the rats, so he instead only kills the bad kind of rats and lets the "good" rats live, in a sort of multi-generational rat breeding program. St-George says that he has been doing this for many years, and his father before him, and his father before that. Jack asks, "how do you know the rats aren't breeding YOU?"