In the sweltering summer of 1518, one woman stepped into the streets of Strasbourg and started dancing—and didn’t stop. Within days, hundreds had joined her in an unstoppable, chaotic, and downright deadly dance-a-thon that baffled doctors, terrified townsfolk, and left historians scratching their heads for centuries. Was it mass hysteria, moldy bread, or the world’s worst flash mob? Find out in this bizarre tale of history’s strangest boogie fever.