Revealing mistake: When Jason climbs onto the rail of the fire escape, it is not attached to the wall - intentionally, it has not broken - but then in another shot, two seconds later, it 'breaks'. It pulls out of a visible hole in the wall, although it was never actually attached and there was no hole before.
Revealing mistake: Just as Jason is returning to the car from the train station after dumping the bag in a locker, spectators can be seen watching the filming, which was apparently done on the sly and without consent. Nonetheless, the onlookers did notice the film shoot and followed the actors' actions, who are not doing anything in the scene to draw attention to themselves. Watch the black man to the left of Jason in the background, he follows the scene and his head turns as he watches. Then look behind Marie right after that and there are 2 or 3 people watching as well, in the background. This is very visible and very distracting.