Continuity mistake: In the scene where Willow and Tara are at the old High School looking for Riley, Willow uses magic to light up the hallway. Tara then asks Willow how she did it. As Willow tells her that she taught her, she tucks her hair behind her right ear. Then after Tara says, "I taught you teeny Tinker Bell light", Willow's hair is hanging back down over her right ear.
Continuity mistake: When Buffy, Willow, and Dawn are discussing Riley's problems in the bedroom, Dawn's hair shifts from over her shoulder in the long shots to behind her shoulder in the closeups. (00:16:45)
Other mistake: Towards the end of the episode when Spike tells Buffy to stake him and removes his shirt, you can see that he has a tan on his upper back/neck to his hairline from wearing a t-shirt.
Visible crew/equipment: When Harmony sits down opposite the operating table, behind her in the glass there is a reflection of a boom mike.
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.