First Date - S7-E14
Other mistake: When Buffy, Spike and Principal Wood are driving, how does Principal Wood notice Spike in the rear view mirror if vampires don't cast a reflection?
Lies My Parents Told Me - S7-E17
Other mistake: Robin uses the song that Spike's mother sang to him to provoke him into attacking him. The song is played on his computer through Apple's media program "iTunes". He clicks his computer's mouse to start the song, but when we see the monitor the cursor isn't placed on the Play button. Robin doesn't jostle the mouse when he presses it, it remains completely still on the desk. And the only way to play a song through iTunes using a single mouse-click is by clicking on the Play button.
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.