I saw an advert for a film on my rental DVD which i though was called Sorority. Apparently not because I looked it up. It has to have been released with in the last year. They basically play a prank on one girl (1) where one of the others pretends to be dead. Well it all hideously goes wrong when girl 1 decapitates prank girl. So they then bury prank girl and then a year after someone comes along and starts murdering them all