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That Scream Really Did Curdle Your Blood

Researchers find a physical basis for a popular metaphor.
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A scene from the aptly-titled Scream. (Photo: Susana/Flickr)

A scene from the aptly-titled Scream. (Photo: Susana/Flickr)

"Bloodcurdling" is a particularly vivid metaphor. Describing a horror movie as scary is one thing; referring to it as bloodcurdling implies a different degree of discomfort.

Well, it turns out the expression is based on an actual physical phenomenon.

Researchers writing in the British Medical Journal report that watching a fear-inducing film apparently creates a certain level of coagulation of one's blood—although, thankfully, not enough to cause actual clots.

The new study featured 24 people, all 30 years old or younger, who were recruited among the students, alumni, and employees of the Leiden Medical Center in the Netherlands. All watched both the 2010 horror movie Insidious, and the 2014 documentary A Year in Champagne. The screenings were one week apart, at the same time of day (early evening).

Blood samples were taken from each participant just prior to watching the movie and immediately afterwards. Researchers looked for markers of blood coagulation activity.

They found levels of a key coagulant factor increased in 57 percent of participants as they watched the horror movie, but only in 14 percent during the documentary.

The researchers, led by Leiden University epidemiologist Frits Rosendaal, report that, "although the coagulation cascade was influenced by acute fear, this did not lead to the formation of thrombin"—an enzyme that plays a key role in activating blood clots.

Why would acute fear activate the coagulation system? "This poses an important evolutionary benefit," the researchers write, "by preparing the body for blood loss during life-threatening situations."

Beginning the coagulation process, but not moving to the point of actual clotting, seems a very smart way to react to threatening circumstances. And the body, of course, does not know that the knife-wielding guy is a fictional character.

The researchers concede it is "not immediately obvious" how these results could lead to medical treatments. But their findings are a reminder of the wisdom of the body, and of the physiological basis of so many popular expressions.

I can't help being fascinated by the latter, as messing around with words is in my blood.


Findings is a daily column by Pacific Standard staff writer Tom Jacobs, who scours the psychological-research journals to discover new insights into human behavior, ranging from the origins of our political beliefs to the cultivation of creativity.