On a hot July day in 1518, a German housewife named Frau Troffea stepped out of her home in Strasbourg and danced in the streets all day. She suddenly started to hop and was unstoppable, ending up with bruised and bloody feet. The other residents formed a crowd around her, and many joined in the dancing for long periods, seemingly without reason. Seeing this spectacle, the town built a stage and hired professional dancers and a band so that people could dance to lively music. But soon, the dancers began to collapse from exhaustion, and some even died from strokes and heart attacks. Eventually,…