Deliberate mistake: Every time the commandos are seen in the early episodes of this season (The Freshman and Fear, Itself) they wear ski masks to protect their identities. Starting in The Initiative, they stop doing this. The reason is that the audience needs to be able to identify the different commando characters, but it's still a discontinuity.
Buffy The Vampire Slayer (1997)
1 mistake in Season 4 generally - chronological order
[After saving Giles from a vampire.]
Spike: Awww, poor Watcher. Did your life flash before your eyes? Cup of tea, cup of tea, almost-got-shagged, cup of tea?
Band Candy - S3-E6
Trivia: The accent that Giles uses as his teenage self is Anthony Head's natural accent.
Question: Specific answer needed, not a general "dialogue is sometimes re-recorded". Near the start of this episode, Buffy's talking to Giles about the significance of the earthquake. Buffy's dialogue sounds completely normal and recorded at the time, but all of Giles' dialogue is dubbed. I can only think he had a sore throat that day or similar, but does anyone know the specific reason he did his later?
Chosen answer: He had larangitis and because of the shooting specifications they had to have him shoot the scene with a bad throat, they then re-recorded his lines and dubbed them. At various points during the scene and indeed the episode you can see him touch his throat or rub it.