Continuity mistake: When Oz turns back into a werewolf, he chases after Tera. She hits him with a chair and he falls to the ground and passes out. We then see The Initiative show up and learn that Riley has shot Oz with a dart (it's sticking out of Oz's side). But two shots earlier the dart wasn't there.
Continuity mistake: When Oz shows up at Buffy and Willow's dormitory, Willow has a lump or a pimple above the left corner of her mouth. It disappears later in the episode when she's talking to Buffy about her feelings for Tara and it returns at the end when she and Oz are in his van.
Continuity mistake: Buffy gets a massive scar on her head from fighting with Adam. This scar changes size at least twice throughout the rest of the episode.
Revealing mistake: After Buffy leaves the cave where Adam kills Forrest, she trips and falls down a horizontal slope. She then rolls over some rocks and one of the rocks wobbles.
Continuity mistake: We see Xander lying in bed with his chest and stomach uncovered. But when Anya comes in and starts talking to him about checking in at the unemployment office, his bed sheets are suddenly pulled up covering his chest and stomach.
Plot hole: Willow hacks into The Initiative's computer system and discovers air ducts and electrical conduits leading to Adam behind 314, but the room doesn't show up on the schematic. It seems unlikely that nobody who didn't know about Adam would have noticed this and investigated.
Revealing mistake: In Xander's dream, when he climbs into the back of the ice cream van, for a split second before the window goes out of view the backdrop cuts out and the blue screen is visible. Only visible in widescreen version.
Continuity mistake: When the group is debriefing about their first Dracula encounter at Giles', Anya is sitting on the sofa with her hands crossed on her lap. In the next shot she has her arms straight with the palms of her hands on the sofa cushion, fingers towards the back. (00:11:25)
Visible crew/equipment: When Riley goes to Spike's crypt to ask him for information about Dracula, the microphone appears in the upper right hand corner of the screen. (00:17:55)
Continuity mistake: After they finish dinner, Joyce says to Buffy that she'll have to get used to her not being around anymore because it gets so quiet. After she says this, her plate disappears.
Continuity mistake: The morning after Buffy is bitten by Dracula, her house address can be seen as "1313" instead of "1630."
Visible crew/equipment: When Willow and Tara are talking about Dawn, just as Willow turns around from hanging her picture to say "help?", a boom mike drops in from the top of the screen. (00:18:35)
Audio problem: When Joyce is about to leave for the pre-show, we hear Xander say "Have fun, but not too much fun", but his lips never move.
Continuity mistake: When Xander is shot by the demon's lightning rod, he falls on a heap of black trash bags. When he is helped to stand up, different bags, pink and white ones, are visible instead. (00:11:30)
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)
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.
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.
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.