Continuity mistake: When Foghorn Leghorn slips an egg into Miss Prissy's nest, you can see that there is nothing on the wall of the chicken shed, but when one the other hens says "A little baby rooster!", there are now nails on the wall.
Continuity mistake: In the first close-up of the big evil that is Billy's brother, Lee Van Cleef's face is lit under a totally different light (when he says "It ain't the money that Brigade wants. Not the money at all"). (00:50:05)
Other mistake: A Telechron electric clock on the fireplace mantel keeps time even though the power has failed.
Continuity mistake: When Sylvester is looking through the window with his binoculars, he looks at Spike and you can see there is a bowl with a bone next to his kennel. But when Sylvester sneaks past Spike's kennel after entering the yard, the bowl has gone.
Continuity mistake: In the opening scenes, the panoramic view of the Larkin homestead shows Lorenzo's "Gummint" Ford sitting with its hood up, days before he has been assigned to the case.
Revealing mistake: Near the beginning, when police Lieutenant Rowan is inquiring on the death of Ken Drake, there are only 4 men in the room, all facing one another in a wide shot. The camera cuts to a close-up of Dr. Bradford for a couple of seconds, and there is a distinct puff of cigarette smoke passing behind him, but none of the characters in this scene are smoking. Lieutenant Rowan does smoke later in the film (in fact, he's the only character who smokes), but he's not smoking in this early scene. Apparently, the close-up of Dr. Bradford was borrowed from omitted footage in which Lieutenant Rowan was smoking.
Factual error: It appeared that, during the engagement with the Serapis, every hit by either ship's guns resulted in an explosion and fire. Unfortunately, explosive shells wouldn't be used on shipboard (aside from bomb vessels) until the next century.
Factual error: Karnak was an Egyptian city, not one of their gods.
Continuity mistake: The car is out of gas, and Sylva Koscina gets impatient. As the shot changes, Walter Chiari's arm is on top of the car door (it wasn't in the first shot) and Dorian Gray crosses again her arms on top of the bag - assuming the same pose she already had. (00:17:00)
Continuity mistake: Christopher Lee looks outside his useless nephew's room and spots two hot Swedish girls. Renato Rascel has a bottle of wine in hand and walks towards him, but the bottle is gone when he tries to stop him. (00:23:40)