Continuity mistake: When Wolverine returns to Storm and Jean, you can see no-one is in his immediate vicinity. A couple of shots later, Callisto and Annalee are standing by the tunnel entrance, a few feet to Wolverine's left. (00:17:05)
Continuity mistake: When Wolverine returns to Jean and Storm after finding Cyclops, he is standing in the opening of the tunnel. When the shot changes, he is standing near the ladder that was several feet behind him in the previous shot. (00:17:05)
Continuity mistake: When Rogue is flying Gambit back to the mansion, the green sides of her uniform above her belt are incorrectly colored yellow, and Gambit's neck is bare, when it should be colored black because of his headgear. (00:16:14)
Continuity mistake: When Rogue is checking on Gambit, the black X's on a red background on both of her jacket sleeves are colored entirely red. (00:16:02)
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 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 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 When the shot changes to them walking past it, the opening has been replaced by a wall with newspaper clippings and a painting on it.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: 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 Jean is first shown in her dress, it is a solid pink color. When she is walking down the sidewalk on her date with Cyclops, the midsection of her dress is now a lighter shade of pink than the rest. (00:04:34 - 00:05:18)
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 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 Jean Grey is first shown standing in Wolverine's doorway, her arm is resting on the door with her elbow level with her shoulder. When the shot changes, her elbow is now level with her breasts. (00:04:34)
Continuity mistake: When Sabertooth is attacking the courtroom, he knocks out three guards with a chair. A couple of shots later, only one guard is on the ground, and when the shot changes again, none of the guards are on the ground anymore. (00:11:15)
Continuity mistake: When Magneto is saying "Mutants will come to me by the thousands," he raises his right fist up near his face. He then begins lowering his hand, and when the shot changes, it is instantly down at his side. (00:20:29)
Continuity mistake: When Xavier is saying "We cannot afford to lose again," his fist is raised, and Storm is leaning over him. When the shot changes, his hand is resting on his hoverchair, and she is standing upright and further away from him. (00:20:05)
Continuity mistake: When Storm is saying "We failed, Professor, together," her lips are red. When the shot changes, her lips are brown. (00:20:00)
Continuity mistake: When Magneto topples Xavier out of his hoverchair, there are two white rectangles on the hoverchair that briefly turn yellow. (00:12:11)
Continuity mistake: After Wolverine says "Let's go kick his butt," he turns his head and you can see his ear changes color from white to the same color as the rest of his flesh. (00:04:15)
Continuity mistake: When Xavier says "Homo superior," his left hand is raised. When the shot changes, his hands are clasped together on the desk in front of him. When the shot changes again to over his shoulder, his hands are nowhere to be seen. (00:03:58)
Continuity mistake: When Xavier says Magneto believes mutants are the next stage in human evolution, the gray nameplate on his desk is centered. When the shot changes, it is now colored brown and has shifted to Xavier's right, near the computer monitor. Additionally, a folder appears on the desk between shots. (00:04:01)
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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