Factual error: One zombie, who's rotted away all his organs, has two eyeballs looking good as new. Even if eyeballs didn't rot, they would fall out with nothing to hold them in. Just like the half of a woman zombie that talks with a soft sultry voice but with rotting or missing vocal cords.
Factual error: The fence surrounding the HARP facility that Remo and Conn break into is supposedly electrified. Not possible - it is a standard chain link fence affixed directly to aluminum posts driven into the ground. If it were electrified it would have to be insulated from the posts; the way it is shown in the film, the electricity would shunt into the ground. When the front-end loader hits it, a plume of firework-like sparks erupts from the point of impact. Also not possible - there was nothing in the bucket of the loader to detonate and the metal hitting against the electrified fence would, at most, cause some small electrical arcs.
Factual error: Clocks usually mark the hour with their first chime. The one in Granville and Baxter's office starts striking in the seconds leading up to midnight, even though its hands are showing the time as still before the hour.
Factual error: There is a scene in which the Catholic high school boys are lined up to go to Confession to a priest. One of the minor characters is a compulsive masturbator, a recurring gag in the film. He is trying to estimate how many times he has wanked since his last Confession, and Kevin Dillon's character takes out a digital calculator to help him figure it out. The film is set in 1965, about 8 years before personal calculators hit the market. (I was precisely the age of the characters in 1965, and we would have sold our souls to the devil for such a device. It was still science fiction!).
Factual error: The supercharged "Honda 750" motorcycle is actually a Honda Rebel 250.
Factual error: Harlan's car has a Roots style supercharger. They can't be "turned on and off" as shown. There is no carburettor or fuel injection lines shown between the scoop and the compressor.
Factual error: When Cressner falls and lands on the horn, it makes the same pronounced honk sound as when he had honked it at Norris. In reality this wouldn't be possible because the bell of the horn was compressed on landing when Cressner threw it out the window earlier, so the sound would've been higher pitched, if it was still able to make a noise at all.
Factual error: Quatermain and Jessie are on the roof of the caboose of the train. The train engineer slams on the brakes because there are elephants on the tracks. Instead of being flung forward as the train slows, Jessie is flung towards the rear.
Factual error: When Anthony Michael Hall is being pursued by the police, they have the logo of City of Los Angeles, but this takes place in Chicago. (01:18:40)
Factual error: During the scene where the laser is used to heat the popcorn in Hathaway's house, the laser hist the ground, works its way up the side of the house and then settles on the window. At that point it stops moving. This seems impossible since the laser is being fired from a moving airplane and would constantly need a slightly different angle in order to keep hitting the house in the same spot.