This Horror Film Really Does "Curdle" Human Blood

Christian Sager

"Insidious." Image via FilmDistrict/Alliance Films
As he crept through the dark fog of The Further, Josh felt his heartbeat slow. Every vein in his forearms pulsed, then fell flat, sending a chill up his shoulders. It was as if his blood had curdled.

Remember "Insidious?" The horror movie from five years ago about a family whose little boy is haunted by ghosts? At the time a lot of viewers found it scary, enough so that it spawned at least two sequels. But now the spooky film by Leigh Whannell and James Wan has been used for science, to prove the accuracy of a term used to describe fear for centuries.

At Leiden University's Department of Clinical Epidemiology in the Netherlands, four researchers have found that watching "Insidious" was associated with an increase in a clotting protein called blood coagulant factor VIII. Published in the Christmas issue of BMJ, the authors claim this research justifies use of the term "bloodcurdling" and could prove that the human body has evolved to prepare for blood loss during life threatening situations, where clots seal off damaged blood vessels.

According to the paper, "bloodcurdling" has been used to describe horror since medieval times. France, Germany and the Netherlands all have similar terms, based on the concept that fear would "run the blood cold" so that it congeals. While several studies have reported that blood coagulation increases with stress, none have addressed the assumed connection between it and horror.

To test this, the researchers showed subjects two films, "Insidious" and a documentary about winemaking called "A Year In Champagne." Based on their very own custom fear scale, "Insidious" received a 5.4 rating out of 10. The documentary received a 0, qualifying as "no fear at all." Participants only gave "Insidious" a fear score as high as 8, leading the authors to admit they had room to enhance the fear of their subjects. Precautions that may have led to this dilution of horror included not showing the movies during a full moon or on Friday the 13th.

Blood samples were drawn from the viewers within 15 minutes before and after each movie. Before both movies the groups had similar levels of coagulation factors, except for two hemolytic anemics and someone who fainted when their blood was taken. These participants were excluded from the final analysis, where coagulant factor VIII was found to be higher in 57% of the participants after watching "Insidious." In comparison, only 14% had higher levels after "A Year In Champagne," while 86% saw their levels decrease.

The paper noted however that other clot-forming proteins seemed unaffected, so while coagulation may be triggered by acute fear, it doesn't lead to actual clot formation. Regardless, the authors feel that using the term "bloodcurdling" to describe fear is now fully justified. Clearly more research needs to be done. What should they watch next to get closer to a fear rating of 10? "The Exorcist?" "28 Days Later?" Perhaps "Shaun the Sheep?"