Deliberate mistake: When Willow and Jenny go out to the parking lot only to discover vampires converging on the school, pay attention to the extras. You can make out some of the same extras in different shots coming from different directions. (Most notably, you can see a woman in a long black-and-white skirt coming from the direction of the parking lot, then a few shots later, she's suddenly over in the football field coming from there.) They obviously reused extras in different shots to "pad out" the crowds.
Buffy The Vampire Slayer (1997)
1 deliberate mistake in Prophecy Girl - chronological order
Continuity mistake: When Buffy is talking to Riley, she puts the scarf on her head, on his hand. He talks to her and says "Maybe I am the bad guy," and in the next frame her scarf is back on her head again, then off again in the next frame. (00:24:20)
School Hard - S2-E3
Vampire: And when I kill her, it will be the greatest event since the crucifixion. And I should know, I was there.
Spike: You were there?! If every vampire who said he was actually at the crucifixion really was there, it would've been like Woodstock!
Once More, With Feeling - S6-E7
Trivia: In 'Once More, With Feeling' the man singing the mustard song is David Fury, the co-executive producer.
Question: At the last moment before leaving for good, Angel pauses to tell Buffy "I don't like him" [Riley], to which she replies with a large smile "Thank you." Why does she take this comment surprisingly well? From an ex boyfriend to her new boyfriend? It's not like it sounds like a friendly warning of any sort, nor a joke given the tense situation between the two guys in the episode. And the smile on Buffy's face does not make her response look ironic either, more like loving/caring. Is that a cross over reference to another dialogue in the Angel series?
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.