Factual error: The "big giveaway" that happens at 9pm across the whole country would have to happen at least five different consecutive times due to time zones. The "big giveaway" in the most eastern time zone would be successful, but further west it would be earlier than 9pm.
Factual error: At the end of the film where the blinded Michael is swinging his scalpel aimlessly, it makes loud "swooshing" sounds. This is pure fantasy. I have personally mimicked what Michael did using similar small scalpels and even larger knives without almost no sound when swinging them.
Factual error: When the house explodes, the only survivors were Private Cooper and the dog, who were hiding in the cellar. With an explosion big enough to destroy the house, the cellar would have been destroyed too, if not from the fireball then definitely from the shockwave. (01:35:00)
Factual error: As Frederick is explaining to his guests how to use their .45 automatics, he fires one round at a near-by vase, shattering it. However, it leaves no bullet hole in the wall directly behind the vase.
Factual error: The main character of the movies buys a pistol that is a 1911 Colt, which fires the .45 round. However, when the police show up at the warehouse, and see the shell casings, they mention as belonging to a .38.
Factual error: When they are driving in the convertible, before the tarantula attacks them with the stones, if you look at their hair, it's not moving with the wind. If they were driving a convertible that fast in real life, it would.
Factual error: When the Security Guard in the pump room gets bitten on the nose, he starts shooting with his revolver (a SIX shooter). Count the bangs. He manages to fire SEVEN times. (00:39:45)
Factual error: As the film itself notes, the major action starts in spring 1818 and continues for several weeks if not months. However, many of the trees remain leafless and the weather is nothing like the norm in spring and summertime Tennessee.
Factual error: When Roland is walking in the pouring rain and talking about killing the T-Rex, he has his gun slung over his shoulder vertically and barrel-upwards. If you were to do this in real-life in a tropical rainstorm for very long, you would run the risk of water entering the barrel and causing problems with the gun. And as a professional hunter Roland would know better. (01:07:50)
Factual error: Paris was surrounded by the German army on September 20th 1870, until January 1871 due to the aftermath of the Franco-Prussian War. This was an obvious danger after the defeat of the French army on September 2nd. No-one in Paris, however, seems to notice. (01:10:25)
Factual error: Throughout the movie, as the train speeds through the starry night, the constellation Orion is recognizable (presumably rising) on the horizon. Oddly, Orion never rises any higher as the night progresses. Also, at the latitude of the southern U.S., the constellation would not rise (or set) vertically as shown but would be tipped at a considerable angle.