Revealing mistake: When Tara is being chased by the monster and she falls, she says a spell and white smoke comes out of her hands but it is coming out of the sleeves of her shirt, the way she holds her hands up suggests this as well.
Revealing mistake: When Jonathan assists Buffy at the beginning of the episode, he enters through the glass ceiling of the mausoleum, which shatters into squares. Although the audio is the sound of glass shattering, the pieces of "glass" flutter down, revealing that the squares are paper - simply for the safety of the actor during the stunt. (00:05:00)
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.