To counter the pervasive influence of religion in our mountain hometown, my father once loaned me his copy of Mark Twain’s satirical Letters from the Earth. A decade later I encountered Twain’s barbed commentary on a famous line from the Sermon on the Mount. To a character who claims that God would care for a poor kitten because “not a sparrow falls to the ground without His seeing it,” Twain has his skeptic respond, “But it falls, just the same. What good is seeing it fall?” America’s greatest humorist has always been its greatest skeptic. How startling, then, to find the same man so generous toward the work of spiritualist mediums in Deborah Blum’s Ghost Hunters, a portrait of 19th-century interest in what we would call the occult.