Bad language is probably the main reason for the "R" rating. Most expletives are obscenities used by the least-likable member of the group, but other protagonists use occasional obscenities. This movie has a lot of PG13-grade cussing, also. There are probably around eight or nine "A" words, and almost as many "S" words. The movie isn't continuously violent, but there are three scenes where the violence gets gross. One guy gets hooked in the throat, and then dragged off by the hook in his neck. Another guy gets hooked in the midsection and blood seeps out of his mouth. One character's blood is seen splashing against a glass door, then you see her getting dragged off by a hook. Those three scenes are the only ones that get really graphic. If you could handle the violent scenes in Final Destination, you can probably handle I Know What You Did Last Summer.