Other mistake: The trees that the brainwashed Wolverine slices down, while chasing after Kitty, fall to the ground too slowly. They should fall quickly as a large, heavy object would, but instead float down like a feather.
Other mistake: The guitar next to Rogue's bed has position markers on all of the odd-numbered frets, beginning with the first. Position markers on guitars start on the 3rd fret, and sequentially follow on the 5th, 7th, 9th, 12th, 15th, 17th, 19th, and 21st frets (and 24th where applicable).
Strategy X - S1-E1
Other mistake: When Nightcrawler pumps his fist in elation while standing in front of the mirror, his arm casts no reflection. (00:09:52)