In 1942, physiologist and Harvard Medical School researcher Walter Cannon published an academic paper with the sort of title you’d expect from a direct-to-video schlock horror flick: “Voodoo Death.”

Cannon was entirely serious, though. In the paper, he argued that historical accounts of supernatural deaths, including those supposedly brought on by voodoo curse, weren’t supernatural at all. Instead, Cannon theorized these victims might literally have frightened themselves to death.

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Cannon was the scientist who coined the phrase “fight or flight,” a concept that is still commonly used as a shorthand for the variety of biological changes our bodies undergo when confronted with a stressful situation. So he clearly had insight into how we react to terror.

“Fear, as is well known, is one of the most deeply rooted and dominant of the emotions,” he wrote. “Often, only with difficulty can it be eradicated. Associated with it are profound physiological disturbances, widespread throughout the organism. There is evidence that some of these disturbances, if they are lasting, can work harmfully.”

At the time, Cannon speculated that abject fear can send a person’s fight-or-flight response into overdrive, triggering a flood of hormones that could—under the right circumstances—cause the body, and in particular the heart, to become fatally imbalanced. He also theorized that fear and isolation could drive someone to avoid food and water, further sinking them into an early grave.

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Contrary to what you might expect, the doctor’s theory wasn’t laughed off as ridiculous, thanks to his well-established reputation. But it would take decades of further research into how the cardiovascular system works before we could really understand how fear and stress can overwhelm the body. And it wasn’t until the 1990s that doctors finally uncovered and named the heart condition that might be the most likely diagnosis of Cannon’s voodoo victims—one capable of killing perfectly healthy people.

Our latest video (watch above) explores the phenomenon of fear-induced death, including this mysterious heart condition. Happy Halloween!