The car the sisters are driving is shown passing an electrical box on the side of the road twice while driving into the town.
When the woman is bludgeoned her blood is blue.
When Abby and Megan are eating in the diner, the red Coca-Cola logos on their cups are painted over with red marker (apparently so as not to give Coke free advertising).
(at around 23 mins) Some crew members can be seen on the car's reflection.