Other mistake: When Buffy and Angel escape from Spike, Dru and the Judge they jump down into the sewer, then run all of five metres before going up the ladder to escape. When they come out of the sewer they are in a very open area with the factory nowhere in sight. They have not travelled far enough for this to be the case. (00:39:15)
Continuity mistake: Near the beginning when Buffy and Willow are talking about Willow getting together with Oz, Buffy's hair is in front of her ears. Then she turns to face Willow to say, "You think he's too old 'cause he's a senior? My boyfriend had a bicentennial," and in that shot change, her hair switches to behind her ear then goes back to being in front of her ears in the next shot without her every touching her hair.
Character mistake: In this episode, Buffy says that Drusilla could be alive because they 'never saw her body'. Drusilla is a vampire; if she was dead, there wouldn't be a body to see - as the slayer, Buffy knows this.
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.