(at around 1h 3 mins) Both times Trevor reads the sheet of paper with Sage's address, it says #202. When he enters her place, "206" is on her door.
(at around 53 mins) When Trevor is "giving himself in" to Sage, she is lying on top of him even though only moments before he had several acupuncture needles in his stomach.
(at around 3 mins) In the beginning when the car is sinking, the left windows on the car are opened, but when the car sinks those windows are closed.
(at around 3 mins) During the full shot view of the car sinking at the beginning of the film, it is clearly raining, as rain drops are seen on the surface of the water. All other shots and scenes show no rain at all.
When Trevor is in the hospital bed talking to the doctor his hands change positions between shots.
(at around 7 mins) During the brain surgery, Trevor grimaces in pain when the surgeon inserts a probe. The brain itself has no pain receptors, so he wouldn't be in any pain.
Bret puts the revolver against his jaw and pulls the trigger. A piece of his forehead explodes when he pulls the trigger. The explosion is consistent with the bullet being fired from behind the back of Bret's head.
When removed from the river, Trevor's head is more or less intact. Not even his hair is apparently disturbed in any way. The caliber of gun that Kirsty shoots Trevor in the head with, at the range she fires it at, would cause extensive structural damage to the head.
Kirsty's motives for killing the five people she kills in the film rest upon her wish to avoid suffering at Pinhead's hands and her anger at her husband for bringing Pinhead back into her life. As well as her anger at him doing so, his motives, and his infidelity. The motives of documented serial killers are never this easy to understand, or justifiable.
In the end of the movie when the car is being pulled from the water you can tell that it was a junk car as it clearly doesn't even have door panels.
(at around 3 mins) During the opening scene, two ramps are visible when the car swerves off the side of the overpass.