When Dr. Swan enters Dr. Colin's hideout for the first time, rats can be seen on the floor, but only in the close-ups. In wide shots there are no rats with Dr. Swan on the screen.
When Jane sits with Christian and asks him for help, her hair changes between the shots.
When Jane pretends to swallow her pills and then spit them out, the pills were red, but when she spits them out, they are white. Then when she shows them to Christian, they are red again.
When Christian says to Jane that's he's listening to her plea for help, she's not holding him anymore, although she grabbed his arm in the previous shot.
Dr. Swan is seen nailing the door to Dr. Colin's hideout, but the nails are just going through the door into empty air, so he's not actually doing anything.
When Dr. Colin enters the room of his first victim, there's obviously a reflector behind him to add to the mood of the scene.
Dr. Colin casually carries the body of his first victim over his shoulder. In reality, it would be a struggle to carry a dead person, no matter how small the person is.
Dr. Swan brings the lamp closer to himself so he can examine the man in Dr. Colins hideout and then after a few moments notices that the man's head is open. He would actually notice it as soon as he brought the lamp closer (and maybe even before that), because the man's head is closest to the lamp.
When Jane is hypnotized for the second time, a shot of the view from a tower can be seen, but on the right edge of the screen someone's finger can be seen holding the camera.
Boom mic visible on left side of frame in wide screen version during earthquake sequence when camera tilts down from ceiling into hallway.