Factual error: There is no possible method of "fusing" the genetic material of a common housefly (Musca domestica) and a human. The housefly has twelve chromosomes, humans forty six. There is no way to combine the two in order to produce a viable organism. Thirty four of the human chromosomes would have no matching chromosome to "fuse" with, meaning the physical characteristics coded by those genes would not form. The Brundlefly would be missing three quarters of his human body.
Suggested correction: There's no possible way of teleporting physical objects either, but it happens in this movie. This is science fiction. These kinds of "factual errors" are not valid.
The film presents no scientific explanation for "teleportation" but does for "genetic merging." Teleportation is possible in this film's universe, but "genetic merging" is impossible in any universe.
Genetic merging is possible in this film's universe; that's the whole point. It doesn't matter if the explanation doesn't stack up, it still works.
Factual error: The mounted machine gun fires far too many shots for the limited supply of ammo it has in the box attached to it.
Factual error: While using the phone in his cell, Dr. Lecktor asks an operator to dial a Maryland area code, but is then connected to the University of Chicago. (00:30:10)
Factual error: When the Delta Force lands on a beach, prior to their assault, their landing craft is lit up like a christmas tree. The commandos wear dark uniforms and have blackened their faces, but they also carry bright white ropes around their chests. Some of them are scuba-divers, wearing yellow oxygen-tanks. In short, in the real world they would have been spotted within minutes.
Factual error: Right before Frank humiliates Dorothy for the first time, he blows out one of the gaslights in her apartment. That is never done in real life, for the same reason you would not blow out the pilot in your stove.
Factual error: Towards the last scene, Howell and Hauer share the same shotgun (Ryder to take pop shots at Jim in the jeep, Jim to ultimately fire three shots to kill Ryder). The shotgun used can hold at most seven or eight shells, not the 12 or more that are fired between Ryder and Jim starting from when Ryder escaped the bus.
Factual error: In an early scene, the high school science teacher produces a schematic diagram of the two nuclear bomb designs created by the Manhattan Project. He says, "Here are two designs based on plutonium." Actually, only the Fat Man bomb uses plutonium. The other, the Little Boy design, uses uranium.
Factual error: When Mitchell is working on his Jaguar, he walks from the bench to the car, places a spark plug, then tightens it with a ratchet wrench. The audio proves, however, that the wrench is set to loosen the plug, not tighten it. (01:11:50)
Factual error: The marines' rifles are supposed to fire "standard armor-piercing rounds", which should have done way more damage than producing a few sparks on the frail sheet metal table in the med bay when Hudson shot the face-hugger threatening Newt. "Standard AP rounds" would have pulverized the table and created a huge hole in the wall behind it.
Factual error: In the scene where Tommy Lee Jones's character shoots down the helicopter. The helicopter has a Canadian aircraft serial number - C-GLCD. Since it's being used by the New York Police Department in New York's Central Park we should expect it to display an American registered serial. (00:53:30 - 00:54:30)
Factual error: After escaping from the back of a NYPD cruiser that apprehended her at the British Consulate, Terry runs into the NYC 57th Street N/R line subway station. In the very next shot, she is running past Cole's French Dip Restaurant on 6th Street.in Los Angeles. The restaurant sign even mentions its location.
Factual error: Ted Bundy is trying to pick up a potential victim in front of a record store, where a poster of Stevie Nicks' album, Rock a Little, is displayed. This scene took place in the mid-1970's, but Nicks' album was released in 1985.