During the summer of 1962, a 15-year-old girl in a Mons hospital began moving her legs in a fast, unbroken rhythmic motion. Despite being fully conscious and trying desperately to stop, her limbs struck the floor forcefully. Sedatives failed, and initial tests showed no traces of poison or viral infection. Soon, the steady ‘tap, tap, tap’ spread to adjacent rooms, transforming the hospital into an unrelenting chorus of motion.

Within 24 hours, 30 cases were reported, reaching 300 afflicted individuals by the end of the week. The relentless movement caused severe physical depletion:

• Feet chafed and bled from friction against the linoleum.
• Muscles grew severely rigid and strained.
• Patients experienced rapid heartbeats and extreme exhaustion.

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The outbreak was marked by a chilling visual contagion. Patients were not moving randomly; if one accelerated, those surrounding them sped up in tandem. The contagion even crossed over to the medical staff. Nurses attempting to steady patients suddenly found their own legs and limbs moving to the exact same rhythm against their will, turning observation into a hazardous risk.

Desperate to find a cause, medical teams tested every possible explanation. They investigated ergotism (fungal poisoning from rye), water pipes, chemical cleaners, and hidden gas leaks—all yielding negative results. Suspicions of encephalitis were dashed by the absence of fevers or blood inflammation. On paper, the patients were healthy; in reality, their bodies were collapsing from total exhaustion.

With modern 1960s medicine completely baffled, researchers were forced to look backward in time. The relentless, contagious movement bore an uncanny resemblance to historical mass hysteria events, most notably the famous dancing plague that struck Strasbourg in 1518, suggesting humanity had encountered this strange affliction before.