"There are many reasons a horror movie can earn an R rating (though its debatable just how much they 'earn' it). On one hand, at least in the U.S., a high body count doesn't necessarily equate the restrictive rating. Yet, a character drops the dreaded 'F Bomb' a whopping two times, and it's a non-starter on PG-13. The ratings system is particularly restrictive on horror which tends to show violence in detail. That means that, more often than not, a horror project is probably going to be rated R, and it's a rarity that a PG-13 one slips through when it should have had the more restrictive rating. The inverse, those R rated horror movies that should have been PG-13 (or PG, prior to that rating's introduction in August 1984), however, has several noteworthy examples. These are the high-profile R-rated horror films that probably wouldn't have scared anyone if they were rated PG-13." - movieweb.com
