In the initial surgery scene, Doctor Génessier makes cuts around the face and eyes of the young woman (Edna). When he and Louise remove the face, there are suddenly marks and a hole cut around the mouth.
At the beginning of the movie when the body is being dragged to the water when it is first removed from the car the corpse is wearing stockings. When the corpse is dragged closer to the water you can see bare legs.
When the doctor parks in front of the morgue, his front wheels are turned left from backing up to the curve. In the next cut, when he leaves the car, the front wheels are straight.
There are actually two different Citroen DS cars used in the film as the Doctor's car. One, presumably a DS21, has two spotlights built into the bodywork by the headlights and chrome trim, including a driver's wing-mirror (see 10:00 as he arrives with no lights and 12:50 as he leaves a few minutes later using headlights and spotlights, another continuity gaff in itself). At 12 :50 and 14:16 the DS with spotlights is seen but at 17:19 it has changed to one with no spotlights and no wing-mirror, presumably a DS19. Though its front plate is "7769-GR75", when the Doctor puts it into the garage, the rear plate reads "2923-GR75" and the assistant's Citroen Diane has the plate "7769-GR75" on the front. At 32:18 the Diane has "2923-GY75" on the rear and at 32:55 the same on the front, which was its registration when first seen near the start of the film. Finally, at 54:49 it's back to the DS with spotlights.
The pupils of a dead body are wide, but Edna's are contracted.
When the doctor is preparing for surgery, he breaks sterility by tying his mask. The unsterile mask should be put on before scrubbing his hands and applying sterile gloves. The theory of sterility is to prevent infection by minimize touch to any surface besides those already sterilized.
When she's not wearing it, Christiane's mask is very thick and heavy and would only seem to cover her face. When she puts it on, however, it is very thin, close-fitting, and seamlessly covers her jawline and the underside of her chin, revealing that the mask itself is a prop while the actress probably wears a combination of makeup and prosthetics.
Through the openings of Edna's bandage there are no signs of a surgery. She's even wearing make-up and lipstick.
Christiane's face was severely burned in a traffic accident, but there are no scars on her cheeks, ears, neck and hands.
When Louise notices a passing airplane, the audio is that of a piston-engined propeller-driven plane, but the airplane shown flying overhead is a jet; its two engines are tail-mounted to the fuselage so would not have the clearance required by propellers.
At approximately 35:48 into the film, Dr. Génessier is carrying an unconscious Edna Grüber out of a room. Just as they're exiting the door you can clearly see a crew member's head move in the bottom left corner of the frame.
In her first scene, Christiane says that her father has removed all the mirrors from the house. But when the doctor carries an unconscious Edna out of the parlor, their reflections can be seen a mirror beside the fireplace.