Book excerpt: Follow scientist Heather L. Montgomery into science labs, forests, hospitals, and landfills, as she asks: Who uses poo? Poop is disgusting, but it's also packed with potential. One scientist spent months training a dog to track dung to better understand elephant birthing patterns. Another discovered that mastodon poop years ago is the reason we enjoy pumpkin pie today. And every week, some folks deliver their own poop to medical facilities, where it is swirled, separated, and shipped off to a hospital to be transplanted into another human. There's even a train full of human poop sludge that's stuck without a home in Alabama! This irreverent and engaging narrative nonfiction book shows that poop isn't just waste-and that dealing with it responsibly is our duty.