Revealing mistake: In the opening shot of the Washington Monument, the monument is very noticeably shaking left and right as the camera pans up (likely indicating that the monument and the background are a composite image). (00:01:00)
No Mutant Is an Island - S5-E4
Revealing mistake: When Killgrave is saying "On your knees," his eyes jump off his face. (00:18:45)
No Mutant Is an Island - S5-E4
Revealing mistake: When Rusty is being brainwashed, his eyes move down his cheeks as his head nods. (00:10:55)
No Mutant Is an Island - S5-E4
Revealing mistake: When Sarah turns off the stove burner you can see that there is an outline of a knob that the animators either forgot to fill in or forgot to erase. (00:05:35)
Revealing mistake: When Rogue is shown tearing off the first portion of the submarine's hull, her feet are missing. (00:17:55)
The Phalanx Covenant: Part 2 - S5-E2
Revealing mistake: When Forge says "That's where we'll begin our assault," his mustache disappears from his face. (00:14:50)
The Phalanx Covenant: Part 2 - S5-E2
Revealing mistake: The shot of Cameron Hodge glaring at Xavier after Xavier asks him about his lack of humanity is a recycled shot from the previous episode. (00:14:30)
The Phalanx Covenant: Part 1 - S5-E1
Revealing mistake: When Beast lunges away from the Phalanx disguised as several people in hazmat suits, after he lands he glides across the grass. (00:08:15)
The Phalanx Covenant: Part 1 - S5-E1
Revealing mistake: The shot of police cars surrounding Sabretooth and him throwing one of them into the air is a recycled shot of the very first shot in the series from the season 1 episode "Night of the Sentinels, Part 1." It's even revealed a few minutes later in the episode that this isn't actually Sabretooth, but a Phalanx facsimile that has taken his form, which makes the fact that Sabretooth's actions are being recycled all the more dubious. (00:01:35)
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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