Continuity mistake: In the scene where the German and Jewish drivers are arguing, there is a corner establishment visible in the background with a sign that reads "wash." In certain shots, a "going out of business" sign is visible in the storefront, while in other shots, with close-ups of two passers-by observing the argument, the same corner establishment is visible without the "going out of business" sign.
Continuity mistake: When Norma and Helen are in the salon, and they are talking about Carrie going to the prom with Tommy, Norma is getting a fancy hairdo done for the prom. But in the next gym scene, she has her plain braids and a cap on. (00:48:20)
Suggested correction: When you watch the movie leading up to that event, it's obvious that Norma is a tomboy, and is always wearing a ball cap and wearing her hair like that. It's who she is and perhaps decided after her hair was done that it didn't feel right and decided to go back to her look.
Factual error: In the cemetery, the skeleton of Gregory Peck's son is far too big to be that of a newborn, which it is supposed to be.
Deliberate mistake: The rail line was supposedly not used in 30 to 40 years, however, in the exterior scenes approaching the bridge where the mile markers were, the tracks are well maintained, has no vegetation, and the rails are shiny, indicating a lot of train use.
Factual error: When the Petrox engineers dump Kong into the pit filled with chloroform they haven't knocked him out - they've killed him. Chloroform vapour is heavier than air so Kong is breathing it in a pretty pure form - and it is lethal in concentrations as low as 40,000 parts per million. In the time it would take to render a gorilla unconscious by this method, it would die. This ignores the fact that liquid chloroform is a severe irritant and a contact poison, and its breakdown products include phosgene and hydrogen chloride, both deadly poisons. They might as well save themselves some time and use that dinky little bulldozer to fill in the pit.
Visible crew/equipment: When the train cars are decoupled, behind the vapor cloud, a person is hanging from the left side of the train car but does not resemble any of the characters in the scene. (01:47:00)
Other mistake: Although the Lieutenant is actually sent to the police station in precinct 9, division 13, the sign over the door states it to be division 14.
Other mistake: The chronology of dates on the teletype printer at the end of the film are not in the correct order. We see "March 13, 1975" followed by "January 3, 1975", which is then followed by two August 1974 dates.
Continuity mistake: When the soldier demonstrates the bazooka on a truck, the projectile hits the front of the truck, but the explosion comes from near the back of the truck.
Continuity mistake: Right at the end when the man takes his mask off, a strand of blonde hair hangs out from the back of "his" head. In the next shot the hair is dark brown.
Continuity mistake: In the scene where Bruce Dern and Barbara Harris are eating hamburgers. He has two on his plate, from a back view she reaches over and takes one. He then removes the cap from the ketchup bottle. The shot switches to a view from his back and the cap is back on the ketchup. He then removes the cap again.
Visible crew/equipment: As Mario emerges into the house from the rain to get the bodies, a crew member is seen when he opens the second door. (01:04:05)
Revealing mistake: In the second murder, the killer of the first one is bashed in the head by a monkey wrench, her head split open. A second hit ensues, but there's no reaction to it, no further spraying or damage, the head itself barely moves, and with delay. (00:04:30)
Other mistake: Legendary wrestler Antonino Rocca makes a cameo appearance in the movie. He is, as correctly listed in the closing credits, one of the "Funeral Attendants" together with Michael Weil. However in the opening credits he was specifically billed as the Funeral Director, which is Ronald Willoughby's role as correctly listed in the end credits. (00:00:50 - 01:45:15)
Continuity mistake: When Christella is slapped by the possessed Ike, her pose changes between shots.
Continuity mistake: When the sniper starts shooting at the audience, at one point he hits a guy in the press sector. However the blood splatter at the victim's shirt appears yet before the bullet actually breaks the window.
Factual error: When a Rear Admiral and Captain are walking together, the Captain's epaulets are the wrong way round. A cardinal sin in the Navy. (01:30:00)
Revealing mistake: By order of the shrewd Harry Webb, the helicopter just destroyed the Cessna on the ground. The two guys decide that they are gonna walk back to civilization. Cut to the vehicle driving to the explosion site, and you can see in the desert sand ahead of the jeep fresh tire tracks from previous takes. And it keeps happening during the desert chase. (00:10:20)