As anyone who's ever sat through a good horror movie knows, the good parts increase your heart rate. But it turns out that watching a horror film can actually increase your white blood cell count. This means if you're attacked by Leatherface, your body can heal itself from (minimal) chainsaw wounds.
Can you genuinely be traumatized by a horror movie? If you're the 22-year-old woman who watched The Exorcist and experienced "intrusive thoughts of demonic possession and flashbacks of the film," then the answer is yes. It seems that some viewers may be susceptible to "cinematic neurosis" if they identify with the "narrative/cultural factors of the film." The paper doesn't cite the patient's particular similarities with the movie…although we highly doubt she was once possessed by Satan.
Dieters, take note: Horror movies may help viewers lose weight. Or as one study discovered, horror movies significantly increased diet-induced thermogenesis (the increase in your energy expenditure above your standard metabolic rate) in 12 healthy subjects.
Horror movies do not increase a smoker's urge to smoke. Smoking in movies slightly increases a smoker's urge to smoke. But a horror movie where the characters are also smoking increases the urge to smoke by 2.8 points--which is considered statistically significant.
Frighteningly, horror (specifically, violent) movies may numb you to other people's pain. "Participants who had just watched a violent movietook over 26 percent longer to help[a woman with an injury] than either people going into the theater or people who had just watched a nonviolent movie."
The reason we respond to horror movie tropes (zombies and vampires) may stem from evolution: In the distant past, we avoided predators with sharp teeth, and "being disgusted by rotten, disease-causing meat is a safety reflex….This is why we are now scared of vampires with pointy teeth and zombies with rotting carcasses."