Factual error: During the scene where everyone runs outside, the Statue of Liberty head crashes into the street. The head is scaled too small and its size can be compared to the people taking pictures. In real life the statue head is large enough for people to walk into (17' from chin to cranium).
Continuity mistake: When Seth has been sliced by the blade, he spits blood that goes all over his face. It then cuts to Hoffman looking at him, then back to Seth, and now the blood on his face has gone. This happens three or four times. (00:05:10)
Factual error: There is no possible way to cause a power line to drop from its support pylons and hit a person on target. These wires are fastened extremely securely, designed to withstand extremely high tension through all kinds of weather, and they are not equipped with some sort of explosive charges to release them.
Factual error: Filbert is in the southwest corner of PA. It is very far out of the way of Harrisburg and completely off the route from Philadelphia to Harrisburg.
Factual error: Benjamin leaves his family at some point after his daughter's first birthday (1970), and definitely before her second birthday. But a 1973-1977 El Camino is parked in front of their house as he rides away on his motorcycle. (02:24:15)
Continuity mistake: As Ben and Jane drive down the road, it is raining. After they hit the ghost, the scene fades to black. When the scene fades back in, it's heavily snowing, and a previously nonexistent thick sheet of snow is covering the ground. As they get out of the car, they start talking. During their conversation, there is a quick cut, and with this, it instantly stops snowing.
Factual error: When Meryl Streep is walking outside and talking to Mrs. Miller about the potential abuses of her son, you can see a basketball court in the background and on the court is a 3-point line. The movie is supposed to take place in 1964 and the 3 point line wasn't introduced until 1979/1980. (01:10:20)
Plot hole: One of the flying dragons impacts the right outer engine of the B-29, and the fire spreads to the right inner engine. The crew lands the plane on the island, and the girls rebuild both engines, despite the fact there are no parts available on the island.
Factual error: A woman is shown receiving electroshock treatment ("ECT") in a hospital scene which took place in 1928. Although chemicals were used to induce seizures in psychiatric treatments at the time, the use of electricity for the purpose was not discovered until 1937 and not used in the United States until 1940.
Continuity mistake: When Dacyshyn drags Mulder by his legs and brings him to the shed, he goes past the tree stump with an axe embedded in it, but in the close-up of Mulder's torso there is some debris on the tree stump and the axe has disappeared, then the axe reappears still embedded in the wood. (01:31:10)
Character mistake: On Taylor's phone it says she dies at 8:32PM, but Beth says 7:32PM, when reading the message. (00:27:05)
Audio problem: Right after Det. Corelli finds the limerick in her apartment, she pulls out her gun and there is a distinct sound of what's supposed to be her cocking the hammer on her pistol. However, Det. Corelli (along with all the other cops in the movie) uses a Glock semi-auto pistol, which does not have an external hammer that can be "cocked." The sound is added artificially, likely for dramatic effect. (01:06:30)
Factual error: At the end of the film, Wyatt and McQuarry each take a briefcase containing $5 million dollars. $1 million dollars in $100 dollar bills (highest denomination in circulation) weighs approximately 22lbs = 110lbs for $5 million. $5 million in $100 dollar bills is also approximately 3445 cu. in. in volume. This would not likely fit in the cases they are carrying, and would not be as easy to carry as they are.
Visible crew/equipment: In the opening murder scene watch when the man is stood outside the connecting train car doors, there is a shot from behind, moving in on him, and if you look out of the left window you can see a set of yellow ladders. This is set equipment and the train obviously can't be moving. (00:02:20)
Other mistake: By the moment that Lea discovers and reads the letter, this, with such typewriting, cannot be written by a six year old boy.
Factual error: Near the end of the movie, a front view of the overdosing/overdosed twins shows Robert putting the dying twin's head on his lap. A close-up of the dead twin shows blood covering most of the left side of her face and a blue tinge on most of the right side, apparently meant to indicate developing livor mortis (bluish color after death). This twin just died, so it is too early for livor mortis to be visible. Livor mortis is not visible to humans until about two hours after death, but the process does begin sooner (about 20-30 minutes after death). Moreover, the writer failed to show the first stage of death - pallor mortis. The twins were Caucasians with blonde hair, so the dead twin would first turn pale (from blood draining from veins in the skin) about 15 minutes after death. The sudden oozing of blood from the dead twin's forehead was also not an accurate portrayal - she was dead, so her heart no longer pumped blood (so gravity takes over, draining blood). (01:39:58)
Continuity mistake: When we first see Agent Holloway viewing the crime scene photos taped to the wall, he is facing camera looking at transparent pictures on a transparent wall (as if we are behind that wall, seeing through it). When the angle changes to see the Agent from behind, the photos are now paper photos on a normal, opaque wall and the pictures are arranged somewhat differently - most notably to Holloway's right near the top where two wider photos are vertically aligned atop and below each other in the second shot when they were misaligned in the first shot by nearly half their width. The transparency versus opaque materials issue is a stylistic choice of the director and not a mistake, but the mismatched alignments is a mistake. (00:11:25)