Scariest and Most gory film you can come up with?

I'm hosting a horror movie night next weekend and I have Paranormal Activity 1 & 2 lined up for the evening, but I wanted a gory film as well. I was thinking Saw, but that was more gore than scare. I would like a movie where things jump out all of a sudden... And rip apart the protagonists best friend in the most gruesome way possible lol. Suggestions?