One of the girls contracts the disease first, and then one by one, they turn on each other. It reminded me of an X Files from many years ago, where everyone was afraid everyone else had the disease. Of course, since they are out in the middle of nowhere, their cell phones have no signal (and I can attest to this having been to a cabin in Gatlinburg, TN recently), so they must search for help by walking through the woods and such. Basically, the horror builds until the bloody finale.
This movie is pure comedy gold, I tell you. While watching it, I thought it was unintentionally funny, because there were serious parts to it. But more often than not, I found myself laughing really hard. I never found myself scared, but I was thoroughly entertained.
After watching Cabin Fever, I checked out the Special Features which included a director's commentary and also a director's short called The Rotten Fruit. The Rotten Fruit was a series of claymation shorts about a British rock band called The Rotten Fruit. Think Aqua Teen Hunger Force, only with a limey accent. I laughed my ass off all through each of these shorts and it was quite apparent to me at that point that the director had a very healthy sense of humor, albeit with a violent bent. Just seeing the boy band C-5 (cherry tomato 5) murdered one by one left me in stitches. This special feature alone is worth the price of admission, but combined with Cabin Fever, its a must have. You won't be frightened, you might be grossed out, but you will definitely be entertained.