Throughout the movie, Walter's Pac-man shirt goes through various stages of cleanliness. It's often seen blood-soaked in one scene only to have spots of blood in the next.
Early in the movie Sara suffers a dislocated right shoulder. When she first wakes up in the hospital after having it reset, she reaches for the nurses button with her right arm and she makes a small cry of pain. But for the rest of the movie she uses her right arm with no indication of pain, when in fact she should be almost screaming from the pain of moving the dislocated shoulder.
Near the finale the killer gets a jar of acid thrown at him, the jar breaks and the acid obviously pours all over him. A minute later the killer is seen without any burn wounds or disfigurements.