In the summer of 2017, Michael Parsons found the urban rat haven of his dreams: A Waste Management transfer station—aka a literal trash heap, aka rat paradise—in Brooklyn, New York. For nearly two years, the behavioral ecologist and visiting scholar at Fordham University had been searching for a place to observe the city-dwelling rodents in their natural habitat. Trouble was, he needed to not only capture the critters and tag them, but then to set them free.