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 When the shot changes to them walking past it, the opening has been replaced by a wall with newspaper clippings and a painting on it.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: 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 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 says to Sabretooth "Be careful what you ask for," his arms are yellow. (00:17:05)
Continuity mistake: When Senator Kelly is giving a press conference to declare his candidacy for President, at the start there is a flag immediately to his right. When the shot changes, after a few seconds the camera pans out and the flag has now moved several more feet to his right. (00:14:05)
Continuity mistake: When the people begin throwing tomatoes at Beast, the judge in the background is sitting down. When the shot changes, he is standing. (00:10:04)
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)
Night of the Sentinels: Part 2 - S1-E2
Continuity mistake: When Gyrich both enters and exits the White House exercise room, the file folder under his arm is the size of a briefcase. When he angrily throws the folder, it is now the standard file folder size. (00:14:45 - 00:15:17)
Night of the Sentinels: Part 1 - S1-E1
Continuity mistake: When Beast tosses Wolverine over the fence, Wolverine's bare arms are the same yellow color as his costume. (00:19:12)
Night of the Sentinels: Part 1 - S1-E1
Continuity mistake: When the arcade manager is confronting Jubilee after she accidentally destroyed the game she was playing, he is several feet away from her, with other patrons between them. When the shot changes, he is suddenly in her face. (00:03:27)
Night of the Sentinels: Part 2 - S1-E2
Continuity mistake: When Gyrich is telling Jubilee that he wants to ask her about the mutants that helped her at the mall, the microphone is up to his mouth. When the shot changes to him tapping his right index finger on the desk, the microphone is nowhere near his mouth. (00:04:27)
The Unstoppable Juggernaut - S1-E8
Continuity mistake: When Juggernaut is stealing the stacks of cash from the bank vault, the money is more yellow in color. When Wolverine slashes open the bags and the cash spills out, the money is now green. (00:12:29 - 00:13:52)
Night of the Sentinels: Part 1 - S1-E1
Continuity mistake: When the guard orders Wolverine, Beast and Morph to halt, Wolverine and Morph are standing next to each other, with Beast behind and between them. When the shot changes, Morph is now behind Wolverine to his left, and Beast is behind Morph and to his left. (00:19:19)
Continuity mistake: When Magneto drops Wolverine, Storm and Cyclops onto the ground, Wolverine and Cyclops are lying mostly perpendicular to Storm. When it changes to a shot of them getting up, they are all parallel to each other. (00:17:18)
Continuity mistake: The prosecutor for Beast's trial is wearing a pink suit. When the unruly civilian is being escorted out of the courtroom, in a wide shot, the prosecutor's suit is now white. (00:08:29 - 00:10:22)
Continuity mistake: When Rogue is interrogating Mystique, she is standing in various places next to the platform depending on the shot. (00:13:45 - 00:14:08)
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)
The Unstoppable Juggernaut - S1-E8
Continuity mistake: When Rogue and Storm first enter the jail, the desk clerk is wearing a blue shirt. When Rogue begins to flirt with him, his shirt is now white. (00:09:48)
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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