Revealing mistake: When Storm is admiring Nightcrawler's body art, there's a point at which you can see the color of the actor's skin in the crease of his neck, because he either sweated off his blue makeup in that spot, or the artists didn't apply enough. There's a point toward the end of the movie where you can see Rebecca Stamos' skin in the crease of her neck as well.
Continuity mistake: When the X-men ship is trying to dodge the rockets, there are a few close-ups of Bobby showing that the seat in front of him is empty. In other shots before and after the close-ups of Bobby, it shows that Rogue is sitting in that seat.
Audio problem: When the last police car arrives at Bobby (Iceman) parents house, it skids up to a halt on the grass out the front of the house. The sound effect used is a car skidding on concrete, not grass.
Continuity mistake: When Nightcrawler tries to stab the president he is in the middle of the table but in the next shot he is at the edge.
Visible crew/equipment: In the jet at the end, what looks like the reflector screen is reflected in Cyclops' visor. This happens in at least two scenes.
Revealing mistake: When the X-Men are leaving the facility at Alkali Lake, they are carrying Professor X because Nightcrawler teleported him. Look closely and you can see Professor X moving his legs back and forth.
Continuity mistake: When Nightcrawler rescues Rogue from falling in mid-air, he dives back into the jet. In the next shot, you can see that the hole in the jet is folding and repairing itself, but a couple of shots later, the hole repairs itself again.
Answer: Presumably he is sensing the presence of Jean/Phoenix.
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