In the opening scene, when Sherry and Jack are attending Mr. Montage's show, Jack's suit, shirt and tie are different when they are seen outside after the show.
During the many gory scenes, some shots of the people are shown with blood all over them. But, in some shots, the blood disappears.
When Jack reads the newspaper announcing the second murder, the articles are obviously pasted onto the paper rather than printed on it; the corner of one article is clearly peeling away from the paper.
In the beginning of the movie, after Montag has chopped his head off with the guillotine, and his body starts grabbing at the head, you can see the hair of the actor behind the guillotine poking out on the right side.
In the restaurant scene when the lady falls on the ground with her intestines hanging out, you will notice that her corpse is still breathing.
When Montag is putting the sword down the second lady's throat during the sword swallowing trick, you can see the "blade" of the sword bend.
When the bleeding woman drops to the ground in the restaurant scene it is obvious, that the carpet around her is covered by a tarpaulin to protect it against becoming dirty.
When the group of people are gathered around the restaurant, the sound effects sound like a much larger crowd.
While appearing on Sherry Carson's show, and repeatedly instructing the audience to "Concentrate", Ray Sager obviously says "Croncentrate".
One of the police detectives states that he followed the second lady (from the sword swallowing trick) from the parking lot to a traffic light before discovering that she was dead - when, in fact, the lady gets into her car on the street just outside the theater while he rushes to his car (that's parked two cars behind hers) on the street. As he tries to catch up to her after she drives away, he briefly drives up on the curb across the street as he accelerates away. Then, she eventually stops her car in what appears to be a wooded area before he comes up to her car to discover that she's dead.