As mentioned in a related article in the scientific form BMJ, researchers at the Dutch University of Leyden, they wanted to see if it is scientifically the medieval theory that fear can “freeze” the blood.
The researchers asked 24 young healthy persons to see a horror movie and after a week of an educational film.
Within 15 minutes before and after each film, the volunteers had to give blood samples, which were analysed as to its coagulability. Participants were significantly more likely to have elevated levels of coagulation factor VII after the horror movie, rather than after the educational movie.
However, no film had no effect on the levels of other proteins involved in the formation of blood clots. Which means that, while fear can cause although blood to clot, it leads ultimately to formation of clots.
In any case, the researchers explain that the coagulation of the blood in response to some event that causes fear can be a positive result of the evolutionary process of the human species, by preparing which means the body for the blood loss during dangerous situations.