Early in the film, a person is shown transporting the film with "Deep Throat" painted one the film case. The case he carries holds only two reels or 40 minutes of film. When the case is opened in the projection room it has grown to a 3 reel case and when the police seize the film a few minutes later, the case is a 4 reel size, the correct size for this film.
Early in the film, an unseen projectionist starts the film and we can see the projected image through the projection room window. He carelessly allows the leader to show on the screen. A frame marked "FOOT" is shown. Unless he is running the film backwards, this is wrong. The beginning of a film is marked "HEAD".