Continuity mistake: In the school used to receive phone calls, a bald man to the left of the guy holding the phone gives a big puff to his cigar, creating a big cloud of smoke. Right afterwards, in a wider shot, all the smoke is gone.
Continuity mistake: When Allison is in CVS, the purse on her shoulder changes between shots. (01:12:05)
Continuity mistake: When the Port Authority police are patrolling the bus terminal in the beginning, a girl in a pink shirt holding a man's hand is coming up behind them. When the two men separate the girl and man are now coming from the opposite direction.
Continuity mistake: When the cops go outside for the first time; Nicholas Cage is holding the paper for the cops who are going with him, in the next shot it's gone.
Continuity mistake: Near the start of the movie when the office worker/security guard feel the 1st plane hit, the security guard is standing just behind the office worker's left shoulder. When the camera cuts to a side view the security guard is standing slightly in front of the office worker with his hand on the water cooler. (00:08:20)
Answer: That cart was very, very heavy.