Other mistake: Despite Lena's cab driver and his wife both being Armenian, the wife's speaking Spanish.
Factual error: Hawking explains how time slows as one approaches a black hole's event horizon. To illustrate this a CGI-animated analog wristwatch is shown ticking away the seconds progressively more slowly. It's the kind of watch that ticks intermittently: once each second the hand sweeps one second-long increment around the dial and then waits one more second to sweep another increment. In the animation, the frequency of the ticks lessens, but the speed at which the hand sweeps each increment stays the same. To be consistent, the sweep-speed needs to slow down just as much as the tick-frequency. (00:36:30)
Continuity mistake: When Jason and The Count duel, the cut on Jason's cheek is already there before The Count cuts him there. By that point, Jason was only cut on the shoulder.
Continuity mistake: When the red haired woman is undressing to enter the jacuzzi to kill the guy, her red dress is either on top of the white robe, or next to it, depending on the shot.
Continuity mistake: It wasn't snowing in the front of the house (e.g, when Ethan, Hallie, and Stephanie were going home; when the ambulance arrived; when anyone came in the front door), but it was snowing heavily in the rear of the house during scenes showing the Christmas tree. (01:18:24 - 01:20:42)
Continuity mistake: The little girl who was missing after falling off the cliff, suddenly shows up again after the evil woman is struck by lightning and is seen standing with the other children to react. But then she's gone again only to then show up with Santa.
Character mistake: Cynthia Kellogg comes forward to voluntarily give information about the James Urbanski case. Detective Nealy tells Kellogg, "As a matter of procedure, I have to inform you of your rights." Kellogg says she didn't do anything so doesn't need a lawyer. Nealy replies, "This is your right" and proceeds to inform her of her Miranda Rights. Miranda warnings are applicable to suspects/defendants who are in police custody (under arrest) and about to be interrogated, not voluntary witnesses. (00:03:02 - 00:03:57)