Continuity mistake: When Jean is walking out of Wolverine's room, part of her dress around her abdomen briefly changes to a lighter shade of pink. (00:04:57)
Continuity mistake: When Jean and Cyclops are kissing after he tells her his mind is on nothing but her, he is wearing a gray suit jacket, when he was only wearing a yellow collared shirt in all previous shots. (00:05:05 - 00:05:48)
Continuity mistake: When Cyclops and Jean are approaching the newspaper kiosk, its opening is facing the sidewalk. When the shot changes to them walking past it, the opening has been replaced by a wall with newspaper clippings and a painting on it. Moments later, they are approaching the same kiosk, after he tells her that his mind is on nothing but her. (00:05:13)
Continuity mistake: After Jean and Cyclops first kiss after she tells him to relax a little, his left arm is around her shoulder and it suddenly jump cuts to his side with his hand in his pocket. (00:05:37)
Continuity mistake: When Leech steps in front of Cyclops and Jean to steal fruit from the vendor, you can see the street behind him. When the shot changes, there is suddenly what appears to be a covered bus stop behind him. (00:05:48)
Continuity mistake: When Leech begins to telekinetically steal fruit from the vendor cart, he is stealing a red apple and what appears to be an orange with a yellow peel. When the shot changes, the orange is now orange in color, and as the two pieces of fruit move towards Leech, the orange is on his right, and the apple on his left. When the shot changes, the orange is now yellow in color again, and the fruits have swapped sides. (00:05:52)
Continuity mistake: When Leech telekinetically splits up the mob, on his left are a man with a light blue shirt, followed by a man with an orange shirt, and man with a light blue shirt behind him. On his right are a man with a green jacket and yellow shirt, a man with an orange jacket and pink shirt behind him, and lastly, a man with a blue jacket and yellow shirt. When the shot changes, the men have not only swapped sides, but now it is two men in light blue shirts in front of the man in the orange shirt, and the man with the orange jacket and pink shirt is now just wearing an orange shirt, and he is standing in front of the man with the green jacket and yellow shirt, and the man with the blue jacket and yellow shirt is in front of him. (00:06:05)
Continuity mistake: When the mob was first chasing Leech, it was six men. When they have reached the subway platform, it is now four completely different men and one woman. (00:06:05 - 00:06:28)
Continuity mistake: When Tar Baby traps the mob inside the subway platform, he seals off the stairs with a wall of tar. When Cyclops and Jean have arrived to intervene, the wall of tar is now in front of the turnstiles. (00:06:24)
Continuity mistake: The picture of Jean and Cyclops Wolverine has framed shows them against a yellow-orange background, and Cyclops' sunglasses are red. When the picture is shown again at the end of the episode, the background is now white and Cyclops' sunglasses are gray. (00:08:14 - 00:20:44)
Audio problem: When Callisto says to Cyclops "away from those who fear us," her mouth is completely closed. (00:09:20)
Deliberate mistake: The video footage Callisto has of the X-Men battling Sentinels at the Mutant Registration Center is just clips from that episode. (00:09:27)
Other mistake: When Xavier is in the War Room with the rest of the team showing where the closest he could pinpoint Cyclops and Jean's location is, he is sitting in one of the chairs positioned around the table. Xavier is paraplegic and usually sits in his own hover chair. While there's no reason he couldn't be sitting in a regular chair, it would be very impractical for him to do so, especially if he's just instructing his team where they need to go. (00:11:07)
Revealing mistake: When Wolverine, Storm, Rogue and Gambit are walking down the stairs to the subway station, you can see that they aren't actually descending the steps, but walking on thin air. (00:11:10)
Continuity mistake: When Gambit is saying "Scott and Jean pick one strange romantic hideaway," the encircled X on Rogue's right shoulder is entirely red, when the X and the circle around it should be black. (00:11:39)
Continuity mistake: When Gambit is saying "Someone may be tracking us," the snaps on both shoulders of his jacket are colored blue, when they should be the same brown color as the rest of his jacket. (00:11:45)
Revealing mistake: When Gambit and Wolverine are pinned to the wall by Tar Baby, Gambit's face somehow gets between the tar and his right shoulder when he is saying "Sticky situation, mon ami." (00:12:01)
Continuity mistake: When Storm is blasting down the door to the small room Jean is captive in, there is a small vent cover to the left of the door. When the shot changes, the vent cover disappears, and then reappears in the next shot. (00:12:33)
Continuity mistake: When the X-Men discover Jean and Annalee in the small room, neither Jean or Annalee are casting shadows on the wall behind them. When the shot changes, their shadows are now on the wall. (00:12:37)
Continuity mistake: When Wolverine punches his lefthand claws into the wall, it is at bottom of a slab of concrete, and to the left of where four slabs intersect. When the shot changes, the puncture is now closer to the middle-right area of a slab. (00:13:16)
Answer: Chris Potter, the original Gambit voice actor, did indeed quit the role in the 4th season. His last episode was The Phalanx Covenant Part 1 so it seems reasonable that Fox would limit the use of the character even though it was recast. It doesn't appear that Potter left the role due to animosity, he stated in an interview that he wished to play Gambit in the first live action X-Men film.
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