Audio problem: At about 18 minutes into the film when Rob, Jason and Hud are on the fire escape talking about Rob and Beth's relationship, Jason says, "You got to learn to say, 'Forget the world.'" But if you look closely at his mouth, you can see he says "Fuck" instead of "Forget". This was most likely censored to keep a PG-13 rating.

Factual error: In the first scene where the Army attacks the monster, the first tank that rolls by is actually a British FV-433 Abbot self-propelled gun made during the Vietnam war years, not an M109 Paladin which most people believe. (Paladin has a longer gun barrel, and has rear turret overhang.) And a few seconds later we see, next to the M1 Abrams, what appears to be an MLRS system firing, but is actually some kind of truck with a multiple rocket launcher, much like the Russian BM21, not the U.S. tracked MLRS system or the M1097 Avenger (which I originally thought it was).

Continuity: When he's walking in the subway, Rob's shirt has a dark triangle of sweat (and dirt) on the back. In one clip the triangle is barely visible and the shirt looks a lot cleaner than before. In the next clip, the triangle is very clear again.

Factual error: After Rob saves Beth from her apartment, they work their way up the leaning building. When they reach the top and they are walking up the stairs to the roof, the stairs are perfectly horizontal even though the building is crooked.

Factual error: I just watched this film on DVD. I know this is a rule of the genre (see 28 Days/Weeks and Die Hard movies) but I find Beth's remarkable recovery from being speared with an iron bar - and stuck there for hours losing blood circulation and muscle cramping - to running around in Central Park helping Rob wholly unbelievable. Maybe she could limp down her building stairs, but whatever physical efforts she does afterwards are even more impossible than those of the monster.