Audio problem: The drummer in Oz's band's movements don't match the song that is heard when we first see them performing at Buffy's house.
End Of Days - S7-E21
Audio problem: When The First lets Buffy get away with Caleb's scythe, Buffy jumps back up the trap door but we don't hear her touch the ground as she lands.
Audio problem: When everyone is in the Bronze - just before the vamps show up - you hear the first line of a song being played, Ballad For Dead Friends by Dashboard Prophets, cut to outside and you see the vamps strolling along and killing the doorman, then cut back into the Bronze and the same line plays again. This is a total error in cutting the show, it is stated there is no live band but still the same line plays twice when that is not how the song goes.
Audio problem: When Buffy kills the vampires dragging Xander at the beginning, we hear two impact sounds but don't hear either of them turn to dust. They were only a few feet away and there was no other sound to cover it up. (00:01:00)
Get It Done - S7-E15
Audio problem: When The First uses Chloe to mimic Buffy, Chloe's lips don't quite match her words.
Audio problem: When Xander, Willow and Ampata meet up at The Bronze, the song the band is playing is at the point of a guitar solo. If you watch Oz (who has already been established as 'lead guitarist') on stage in the background; he's blatantly NOT playing that solo. The hand movements don't match up.
Audio problem: While Faith is stabbing the demon in his apartment, we hear the sound of her knife going through, and him yelling in pain. However, the last sound of her stabbing him comes a little late: The knife isn't even touching him.
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.
Audio problem: When Buffy is about to close the door as she goes into the bathroom, it actually never closes. But we still hear the sound of the door closing. (00:15:20)
Audio problem: When Giles and Anya are talking to the demon, trying to get him to open the portal to Beljoxa's Eye, when you see Anya's face from the side, her lips don't sync up with what she is saying, and sometimes her lips are moving to words when she doesn't have any lines at all.
Audio problem: When Giles and Miss Calender are walking through the halls at the beginning of the episode there's a kid at the vending machine, we hear the coins rattling but he never puts money into the slot. In fact, the money doesn't go anywhere near the slot.
I Only Have Eyes For You - S2-E19
Audio problem: When Giles looks through the window of a door at the high school and sees the janitor yelling at the teacher, the janitor's lips don't match with what he is yelling.
As You Were - S6-E15
Audio problem: When Buffy has just killed the Suvolte demon and Riley is found out to have not told her it was a tracking only mission Sam says something like 'If we weren't under time constraints, I'd rip you a new one.' Riley then says 'Stand down soldier.' Buffy asks Sam, 'Is he your boss?' And Sam replies 'He wishes. We better regroup.' But her lips to not move when she says they have to regroup. You can see her mouth on screen and she is just smiling, not moving her lips at all.
First Date - S7-E14
Audio problem: In the graveyard scene when Cho-Anne says the Cantonese translation of 'I don't understand what any of you are saying', watch her closely in the shot just before it. She starts to mouth part of the line early, but we don't hear it.
Once More, With Feeling - S6-E7
Audio problem: When Tara sings to Willow and sings "nothing i can do", her lips don't move.
Chosen answer: Angel is saying that he is still jealous and Buffy recognizes that this is his way of saying he wishes that they could be together. That is why they both smile.