When the two girls first met the two guys while they were in their cars on the road, what was their goal in enticing the guys to go to the "party" and thus get mixed up in the mess? The only thing I can think of is to release their remains?
shareThe mention at the end that the girls don't remember that they are dead. So in the beginning they really think they are heading to a party and would love these attractive guys to go with them. You can also see some allusion to this in other scenes. For instance, also at the first meeting the guys ask if the party is 80's themed and the girls look confused but then just respond yes.
Also, at the very end, the girls are compelled to speed up and don't respond to the questions from the boy in the back seat. They must repeat thier sequence whether they want to or not.