Nightmares - S1-E10
Revealing mistake: The Master's artificial thumbnail is visibly falling off in a few shots of the opening teaser. (00:01:30)
Tough Love - S5-E19
Continuity mistake: In season 5, 'Tough Love', Glory crushes Tara's hand causing her blood to drip onto the bench. In later shots however, there is no blood on the bench, it is clean. (00:25:40)
All The Way - S6-E6
Continuity mistake: When a vampire kicks through a car window trying to hit Buffy, some shards are still standing in the window frame. The angle changes, and the shards are gone. (00:37:00)
Out Of Mind, Out Of Sight - S1-E11
Visible crew/equipment: At the very end, as the invisible girl gets taken along a corridor by the FBI agents, check the top of the screen - a boom mike creeps in as the agent says his line, then is withdrawn.
Revealing mistake: When Buffy runs in front of the car you can see knee pads on her knees. You have to look quite closely because they are the same colour as her tights. (00:15:00)
Continuity mistake: When Buffy drowns in Prophecy Girl, she falls into the pool with her hair tied in a ponytail and her arms under her. When she is discovered by Angel and Xander, her arms are by her sides and her hair is loose. (00:33:55)
The Harsh Light Of Day - S4-E3
Continuity mistake: When Spike pins Harmony to the wall, his hands change from flat against her to grasping her shoulders, depending on the angle. (00:12:00)
Revelations - S3-E7
Revealing mistake: In 'Revelations' when Buffy and Faith are fighting, the kick Faith aims at Buffy's face right after she says 'We can work this out' very noticeably misses, but Buffy still reacts as though it landed. (00:36:15)
Lover's Walk - S3-E8
Continuity mistake: In the episode Lover's Walk, when Spike is threatening Willow at the factory, in the long shots Willow's hair is up over her face, and in the close-ups it isn't. The pointed bit of the bottle is at the top or bottom in different shots too. (00:19:20)
Revealing mistake: Several times during Spike's escape from The Initiative, his reflection can be seen in the glass. Vampires aren't supposed to have reflections. (00:13:00)
Deliberate mistake: While it is established that Angel doesn't age, it's obvious across both Buffy and Angel that David Boreanaz gets older. More unavoidable than deliberate, but still worth noting.
Checkpoint - S5-E12
Continuity mistake: In the series 5 episode 'Checkpoint' when Buffy has just accidently axed the dummy, watch her blindfold. It goes from being pushed up above her forehead on her hair, to being right down by her eyes. This changes between every shot. (00:27:55)
Life Serial - S6-E5
Continuity mistake: While working at the Magic Box, Buffy's horseshoe necklace constantly shifts between left, middle, and right positions, even within the time loops. (00:20:20)
Revealing mistake: When all the vampires are saying "for the dark", and one gets staked, there's a mark on his shirt where the stake's about to come through before it actually happens. Plus Buffy's hands are in the wrong place for her to have pushed that stake through, as well as there being no stake in her hand when the vampire gets dusted. Not only that, but the mark isn't even close to the vampire's heart to begin with. (00:34:50)
Continuity mistake: When Willow hands Giles the pages she stole from the books of ascension, initially the folded side faces to the left, with loose edges of pages to the right, then in the next shot the folded edge is now on the right. (00:36:25)
Life Serial - S6-E5
Continuity mistake: Warren switches from holding Jonathan's magic bone with one hand to two hands between front and reverse shots. (00:19:10)
End Of Days - S7-E21
Revealing mistake: When Buffy finds Faith and the Potentials in the sewers she throws an Ubervamp across the room. When we see the Ubervamp from behind you can also see the actor's blue boxer shorts sticking out of the Ubervamp costume.
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.