Continuity mistake: The amount of damage to Cyclops' uniform decreases. When his Danger Room session is first terminated, his uniform is mostly missing around his shoulders and chest. A few shots later, the aforementioned area of his uniform is not as torn up. (00:04:15 - 00:04:50)
Continuity mistake: The position of Cyclops' body changes when Jean Grey is cradling his head. At first, he is sitting slightly upright. When the shot changes, he is lying down. (00:04:40)
Continuity mistake: During Gambit's flashback, the chosen one for the Assassin's Guild is shown to be placing their tithe box on the stump of a tree roughly halfway between the center ring and the outer edge. When the shot changes, the tithe box has suddenly moved to the center of the stump, and the tithe box itself is suddenly wider and shorter and has rotated 90°. (00:05:00)
Other mistake: When Gambit is wiping sweat off his forehead, the locks of hair that he is rubbing his fist against do not move. (00:05:20)
Continuity mistake: In the flashback when Gambit runs up to two of his fellow guild members to tell them the others are almost there, he runs up to the one in the blue vest. When the shot changes, he is suddenly facing his brother Bobby. (00:05:21)
Continuity mistake: When the chosen one for the Thieves Guild is called forward to present their tithe, the chosen one for the Assassins Guild can still be seen kneeling before the External. In the next shot when the chosen one for the Thieves is shown arriving on the scene, the chosen one for the Assassins is suddenly back to standing among the other members of his guild. In the next shot, the chosen one for the Assassins is back to kneeling before the External. (00:06:00)
Continuity mistake: When the chosen one for the Thieves Guild tries to present their tithe to the External, he is shown walking right up to the tree stump where he was to have placed the tithe. When the shot changes, he is still walking forward, and therefore should've bumped into the stump. He is saying a line of dialogue as he is walking forward, so it can't be considered an action shown from a different angle. (00:06:15)
Continuity mistake: When the chosen one for the Guild of Thieves drops his tithe box, it lands on the inside of his right foot. When the shot changes, the box is suddenly equidistant between his feet. A couple of shots later, the box has moved away from him, resting next to the tree stump. (00:06:17)
Continuity mistake: When Bella Donna is being selected as the chosen one for the Guild of Assassins, she is flanked by three of her guild members. When the shot changes, the three guild members have disappeared. (00:06:49)
Continuity mistake: When the External selects Bobby to be the chosen one for the Guild of Thieves, she turns his jacket red and his gloves gray and fingerless. When he is shown again a few shots later, his jacket is now green, and his gloves are brown, with only the thumbs being fingerless. (00:06:53)
Continuity mistake: When Wolverine enters the infirmary, Cyclops is resting his right hand on his lower abdomen area with his fingers extended. When the shot changes, his hand is a closed fist and has moved closer to his chest. (00:07:37)
Continuity mistake: When Gambit lands his mini-jet in the swamp, it's in an open area. When Wolverine, Rogue, and Jean Grey find his plane shortly after, it is now parked next to a tree and some foliage. (00:07:48 - 00:08:56)
Continuity mistake: When Pierre is waiting for Gambit in his boat, there is another boat next to his. When he and Gambit take off, the second boat has disappeared. (00:07:55)
Deliberate mistake: When Gambit and Pierre are boating down the river, in the shot of Pierre saying "Yeah, we got word," the trees they pass on either side of the screen are just the same tree drawn repeatedly. (00:08:08)
Continuity mistake: After Jean Grey, Rogue and Wolverine locate Gambit's mini-jet, they land the Blackbird behind a row of plants. When they emerge from the Blackbird, the plants have disappeared. (00:08:55)
Continuity mistake: When Wolverine runs up to Gambit's mini-jet, he puts a considerable amount of distance between himself and Jean Grey, and nearly makes it all the way to the jet and Rogue before the shot changes. When the shot does change, he is suddenly several feet back from where he just was, and Jean Grey is now right behind him. (00:09:01)
Continuity mistake: In the first establishing shot of the Assassins Guild's mansion, there is a stairway leading up to the front door. In the establishing shot of the mansion in the scene where Gambit is in Bella Donna's bedroom, the stairway is missing, and consequently the mansion's porch area isn't as high off the ground. (00:09:20 - 00:13:20)
Continuity mistake: The two assassins standing guard outside the Assassins Guild's mansion have swapped sides when they let Gambit in the front door. (00:09:25)
Continuity mistake: When Gambit first walks into Bobby's cell, Bobby is sitting in a chair up against the back wall. A few shots later, Bobby is sitting in the center of the cell. (00:09:55)
Continuity mistake: The cell that Bobby was held captive in is noticeably smaller after he is set free. (00:09:55 - 00:11:40)
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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