Scary movies and horror stories are sometimes described as "blood-curdling" – and it may be literally true, according to Dutch researchers.
The study is one of the collection of odd-ball reports that appear in the annual Christmas edition of The BMJ.
Researchers tested the idea by getting young adult volunteers to watch a horror movie followed by a "non-threatening" movie.
They measured levels of the clotting protein blood coagulant Factor VIII.
The researchers say they set out on the study because evolutionary theory suggested benefits from fear triggering congealing of blood – to limit harm from wounds.
Similar words to "blood-curdling" are found in many languages. In Dutch it is "bloedstollend" and the French refer to the blood freezing.
The 24 volunteers gave blood samples after watching each movie and also completed questionnaires aimed at confirming whether they found them frightening.
They found that Factor VIII levels increased in 12 volunteers during the horror movie but decreased in nine. In contrast levels fell among 18 volunteers during the other movies and increased in three.
There was no effect on other coagulants.
The researchers, led by Professor Frits Rosendaal, at the Leiden University Medical Centre, Netherlands, report: "Watching blood-curdling movies is associated with an increase in blood coagulant factor VIII without actual thrombin formation.”
Bloodcurdling movies and measures of coagulation: Fear Factor crossover trial BMJ 17 December 2015 [abstract]
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