On a hastily built stage before the busy horse market of Strasbourg, scores of people dance to pipes, drums, and horns. The July sun beats down upon them as they hop from leg to leg, spin in circles and whoop loudly. From a distance they might be carnival revellers. But closer inspection reveals a more disquieting scene. Their arms are flailing and their bodies are convulsing spasmodically. Ragged clothes and pinched faces are saturated in sweat. Their eyes are glassy, distant. Blood seeps from swollen feet into leather boots and wooden clogs. These are not revellers but “choreomaniacs”, entirely possessed...