According to a study at the University of Westminster, watching horror movies can burn up to 200 calories per viewing. That's about as many calories that chocolate bar you are scarfing has.
During a scary movie, your heartbeat quickens, causing your blood to pump faster and raising your adrenaline, just like if you went for a brisk walk. Unsurprisingly, movies that make you jump burn even more calories. Of course, if you are like me and can no longer be scared by horror films, I don't think it has much impact.
The Shining burned the most calories out of the ten films screened, with 184 calories. Of course, The Shining is the longest of all the films screened, beating out second-ranked Jaws by a good 15 minutes.
The top ten calorie burners, according to the study, are:
1. The Shining: 184 calories
2. Jaws: 161 calories
3. The Exorcist: 158 calories
4. Alien: 152 calories
5. Saw: 133 calories
6. A Nightmare on Elm Street: 118 calories
7. Paranormal Activity: 111 calories
8. The Blair Witch Project: 105 calories
9. The Texas Chain Saw Massacre: 107 calories
10. [Rec]: 101 calories
Check out this Telegraph article for a slightly more scientific look at this phenomenon.