Corrected entry: There is a scene in which Denzel Washington is required to shoot a person on a city street who is possessed by a demon. Washingon uses a Glock pistol and fires only one shot. In the scene it is clear after the shot is fired that the gun's slide is in the locked back position (this only happens after the last round is fired. A Glock typically holds between 8-15 rounds). In the next frame, while Denzel is still holding the gun in the shooting position, we see that the slide has been moved forward.
Corrected entry: The narrator along the course of the movie is Denzel Washington, and we're led to believe his character is the one telling the story. But as we've seen throughout the movie, Azazel takes the voice of anyone he possesses. Of course it would be silly to have a cat narrating the film, but Azazel is not in the same body as the narrating voice at the end.