Continuity mistake: When Warren Worthington is strapped to the table, the arm and leg restraints are gold. After the table has been lowered, the restraints are now silver. (00:02:29 - 00:02:56)
Continuity mistake: When the conference chairman is first shown at the podium, there are five microphones attached to it. A few shots later, there are only four. (00:07:55)
Continuity mistake: The trap door that Apocalypse uses to escape suddenly disappears once Wolverine tries to claw his way through it. (00:19:35)
Other mistake: After Gambit explodes the statue that was about to fall on Wolverine, there is no debris shown to be flying around them even though the statue was collapsing towards them. (00:16:30)
Continuity mistake: When the statue is about to fall on Wolverine, his arms are colored yellow. (00:16:25)
Continuity mistake: When the tank is falling through the hole in the bridge, the tank's gun barrels are pointed towards the water. When the shot changes to the tank landing in the water, the gun barrels are pointed towards the sky. (00:09:40)
Other mistake: When the tank falls through the hole in the bridge, the tank's occupants are impossibly shown to be clinging to the edge of the hole at the same time the tank is going over the edge, as if the tank and the occupants were occupying the same space. (00:09:40)
Continuity mistake: When the news reporter is first shown talking about the World Peace Conference, he has one blue eye and one brown eye. For all remaining shots he is in, both of his eyes are blue. (00:07:40 - 00:08:35)
Continuity mistake: When Storm is teasing Gambit for damaging the pool table, she is holding a television remote in her left hand, which is yellow (Storm doesn't wear gloves). A couple of shots later, she is holding the remote in her right hand (she had time to transfer the remote to her other hand, so no mistake there), which is colored correctly. (00:07:35)
Continuity mistake: When Rogue turns her head to face Jean Grey, some of her brown locks of hair turn white. When she turns back to face Gambit, the white locks become brown again. (00:07:20)
Continuity mistake: When Rogue tries to sink the 8-ball, the ball comes to a dead stop just in front of the side pocket. When Gambit goes to take his turn, the 8-ball is suddenly near the center of the table. (00:07:00)
Continuity mistake: When Rogue and Gambit are playing pool and Rogue is getting ready to try and sink the 8-ball, the cue ball is shown to be close to the corner pocket and its rail. When the shot changes, both balls are suddenly further away from the pocket and the rail. It's an instantaneous change, so it can't be a matter of the cue ball rolling. (00:06:45)
Continuity mistake: When Apocalypse is saying "Go forth my horsemen," his right arm is raised up. When the shot changes, his right arm is immediately at his side. (00:06:30)
Continuity mistake: When Cyclops forces his way to the front of the crowd to confront Warren Worthington (Mystique in disguise), the Lady Gardener is standing just behind the mutant with the bowl-cut hairdo. When the shot changes, the two are suddenly standing next to each other. (00:04:30)
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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