People have been using the term "bloodcurdling" to describe feelings of intense fear for centuries. Now, a new study has found that being scared can, indeed, cause your blood to thicken, NBC News reports. Dutch researchers found that a frightening situation—in this case, watching a horror movie—can increase levels of Factor VIII, a blood-clotting agent. "We hypothesized that acute fear activates the coagulation system and that this poses an important evolutionary benefit, by preparing the body for blood loss during life-threatening situations," write the Leiden University Medical Center researchers in the study, which was published in the December issue of the British Medical Journal.
The study used 24 healthy volunteers ages 30 and under. UPI reports 14 of the subjects watched the horror movie Insidious and then, a week later, watched the documentary A Year in Champagne at the same time of day. The order of the movies was reversed for the other volunteers. Blood samples were taken before and after participants viewed the movies. Levels of Factor VIII increased in 57% of subjects during the horror movie, while they decreased in 86% of participants during the documentary. No one in the study suffered a blood clot, NBC notes. While the researchers outline some study limitations (sample size, "the magnitude of fear induced by the movie genre"), they conclude that "after centuries the term 'bloodcurdling' in literature is justified." (Speaking of fear, here's how to cure a spider phobia in 2 minutes.)