Factual error: At the end of the film, when Duchovny and Jones are on the ladder truck shooting the head and shoulders, they are yelling "go go go". They slide down the ladder and the next shot is the fire truck speeding away. Movie elapsed time 5 seconds. It is a physical impossibility for a fully extended ladder to be lowered, retracted and bedded in a span of less than 4-7 minutes. Even if the hydraulic lines are cut, the ladder would remain upright and not collapse/retract. (01:32:59)
Factual error: The aliens are supposedly nitrogen-based, making them vulnerable to selenium in the same way humans are vulnerable to arsenic because we're carbon-based. However, nitrogen atoms don't have the valence real estate to form the long molecular chains critical to the DNA structure shared by terrestrial and alien life (when Ira first analyzes the sample, he finds DNA with 10 base pairs). (01:20:30)
Factual error: Ira says the aliens have 10 base pairs in their DNA and humans have 4 base pairs. Humans have four bases in their DNA, not 4 base pairs (we have over 3 billion base pairs). Not a mistake a biologist would make.