The ancients argued, or so we are told, about how many angels could dance on the head of a pin. This intriguing application investigates more earthly, and more satisfying, questions. (For one thing, they are answerable.) The urge to enumerate is as strong in Homo sapiens as the imperative to name. Indulging our fondness for tallying, How Many? addresses 48 aspects of animal behavior, earth science, and our doings on the planet in a Q&A format that is a surefire remedy against boredom on (say) the long drive to a trailhead. How many tree species populate the Amazon Basin? How many teeth can be found behind the lips of a great white shark, or a rabbit? How many stomachs does a cow contain? How frequently does a hummingbird flap its wings? Without this deck, you may never know.