Visible crew/equipment: When the ambulance is about to crash into the tanker, right before and during the crash a camera mounted (painted white) on top of the cab is seen.
Plot hole: After Abe is shot, an ambulance shows up, throws Sherry in the back and leaves. There is no way that the paramedics would leave without first speaking to the police on site, making sure that no one else there needed medical help and confirming Abe was dead. I've ridden with an ambulance 4 or 5 times and they never stay at a scene less than 15-20 minutes.
Continuity mistake: When the dead girl in a red raincoat appears in the doorway, at first the damage is on the right side of her face, next shot on the left, then in the third shot it has gone back to the right.
Chosen answer: The third day (according to the movie) after someone uses the white light to save someone, is when the devil can step in and try to cause chaos. They did try to explain this in the movie, though it didn't make a lot of sense for anyone with any idea about the subject.