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)
Deliberate mistake: For all exterior shots on the surface of Mars, the crew's "pressurized" space helmets have no face-plates (their faces are fully exposed to the hostile Martian environment). The transparent face-plates they intended to use reflected far too much studio set lighting, such that the glare would have obscured the actors' faces. On a $200,000 budget and a 10-day production deadline, they simply scrapped the face-plates and shot the scenes with wide-open helmets.
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)
Continuity mistake: When Richard Hannay jumps from the Sheriff's window into a passing truck it is full of bales of hay. The next time we see him in the truck it is full of sheep and the bales of hay have vanished.
Other mistake: After the intro, one girl in the bar peeks from the window and goes; "Say, here comes Gordy and Jennie." And indeed the duo is getting off the car and joins them. The problem is, the window is on the opposite side of the entrance and there's diegetic music playing throughout the scene. In other words, she saw them parking to the left, but in a split second they are coming through a door on the right. (00:02:40)
Continuity mistake: When Mama Ape takes Bugs Bunny out of his bed, Bugs is wearing a baby hat, but when Mama is holding him in the next shot, the hat has disappeared.
Continuity mistake: When Stanley is shown around the cake factory he takes his hat off and puts it on a conveyor belt and it is carried into a machine and covered in icing. But in the scene before this with the supervisor saying "and this is the enrobing chamber" you can see his hat come into shot on the conveyor belt already. In the next shot he still has his hat on and only then takes it off and puts it onto the conveyor belt. (00:13:08)
Continuity mistake: When Elvis hands a pair of binoculars to his pappy, you can see there is a swarm of flies buzzing around Pappy, but in the next shot the flies have disappeared.
Other mistake: A police officer fires two shots, hitting a bank robber in the back. The "bullets" do not make holes in the robber's coat. All they do is create two tiny puffs of dust.
Continuity mistake: When Witch Hazel is chasing Bugs Bunny up the castle tower, Bugs throws a stone through the window before Hazel appears from behind the curtains. When we see Bugs dressed up as Romeo, the glass panes have disappeared, and when we see Hazel dressed up as Juliet, they are back again.