Factual error: There's no way that the knife that killed Bob was long enough to go through his body and impale the wall behind him. And a butcher knife cannot "pin" a human body to a wall and just stay put, they aren't strong enough.
Factual error: When they are refuelling the helicopter (as a zombie approaches quietly from behind) the actor has put the gas nozzle not into the hole for the gas tank, but into one of the foot-holes that helicopter mechanics use to climb up to the top of the helicopter to do repairs. It doesn't even fit properly. (00:22:55)
Factual error: The "Cable Junction" in the movie is a transformer junction station built on a rock pile however when you look at it there is no algae or barnacles anywhere on the rocks. This is impossible because algae and barnacles thrive on rocks in sea water.
Factual error: The movie takes place in Chicago, except for one scene that is supposed to be in New York City (when Damien's uncle visits the priest). Two problems. First, as the cab pulls up to the church where the priest is, it goes past a housing project. Anyone who knows public housing construction in New York and Chicago knows that building is in Chicago. Second, when they go out to a trainyard, you can clearly see the Hancock Tower in the background. Of course, that building is in Chicago, not New York.
Factual error: When Rita is in the doctor's surgery for her prenatal visit, the chest X-ray in the background is upside down.