Factual error: When Moira is calling her ex-husband Joe in Edinburgh from the Blackbird phone, she dials a typical U.S. seven-digit phone number (it looks like she dials 555-1238). However, even assuming she wouldn't be required to dial an exit code from the Blackbird, a typical Edinburgh phone number would have more digits, along the lines of +44-131-XXX-XXXX. (00:16:50)
Continuity mistake: After Joe hangs up on Moira, if you look at Wolverine in the background you will see that his face is colored yellow. (00:17:30)
Continuity mistake: At the very end of the previous episode after Proteus had messed with Wolverine's sense of reality, Wolverine is shown whimpering in an open area. When Wolverine is shown at the beginning of this episode still whimpering, he has suddenly moved next to a treeline. Given the state of shock he was in, it's doubtful he would have gotten up and moved. (00:02:00)
Other mistake: When the two civilians are walking past Joe McTaggert's campaign posters, they are shown to be walking unusually fast, almost as if the ground beneath them is moving them forward between strides (similar to as if you were walking on a moving sidewalk inside an airport). (00:03:00)
Continuity mistake: When Moira is saying to Proteus "Kevin it's time to come home," you can see that Rogue is suddenly not wearing any lipstick. (00:04:05)
Revealing mistake: When Proteus is leaving his father's home while possessing the police officer, the green glow of his eyes doesn't stay in place as he is moving. You can see the green glows leave his face and float in midair with the eye slots on the face turning black. It appears that the animators couldn't keep the glowing eyes synchronized with the body movement. (00:07:30)
Audio problem: When Joe McTaggert is saying "If the boy shows up, keep him out of sight until after the vote. If you don't, all of our work will be for nothing," he has suddenly lost his Scottish accent. (00:07:40)
Audio problem: The amount of crowd noise during Joe McTaggert's speech is inconsistent with how many people are shown in attendance. The noise would suggest at least a couple hundred people, but shots of the crowd only show a few dozen. (00:08:25 - 00:10:20)
Other mistake: Moira's arms are disproportionately long when she rescues Xavier from falling into the pit. (00:12:30)
Continuity mistake: When Xavier is speaking to Proteus telepathically, the position of his shirt and jacket sleeves go from being a few inches below his wrist in one shot, and then just slightly under his wrist in the next. (00:12:55)
Continuity mistake: When Proteus leaves the town hall, the door he exits is shown to lead into an alleyway. Moments later when Moira exits through the same door, it is shown to be leading into a corridor in the same building. (00:13:15)
Continuity mistake: The exit door and stairwell outside of the town hall are shown to be at the very edge of the building when Proteus goes through it. When Xavier, Beast, Rogue and Wolverine use the same door and stairwell, the building suddenly stretches on for several more feet. (00:13:20 - 00:13:55)
Continuity mistake: After Magneto crashes through the roof of the U.N. building, the nameplates designating the nations of the delegates have suddenly become blank. (00:02:20)
Audio problem: Magneto's mouth is closed when he says "The mutant race will no longer be managed, mister delegate." (00:02:20)
Continuity mistake: When Magneto forces the Genoshan delegate to sit down, the chairs surrounding him are empty. A couple of shots later, the chairs are occupied. (00:02:35)
Plot hole: Some of the footage Magneto is showing the delegates at the U.N. meeting includes footage Magneto could not possibly have had access to even if such footage existed, such as the X-Men having mission briefings in the War Room, the Morlocks living in the sewers or Warren Worthington emerging from being buried under several feet of snow at his secluded home in the mountains. (00:03:10 - 00:04:05)
Continuity mistake: When Magneto is showing Asteroid M to the delegates at the U.N. meeting, the Genoshan delegate he forced to sit down has either moved to another seat entirely or the people that were sitting around him moved to different seats and other people filled in their seats. (00:04:05)
Audio problem: Fabian Cortez's mouth is closed when he says "Lord Magneto." (00:10:15)
Continuity mistake: When Gambit is trying to distract the Sentinels, both of his gloves are entirely fingerless whereas normally his gloves are only fingerless for the thumb, index and pinky fingers. (00:12:00)
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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