Continuity mistake: In the scene near the end when Faith is putting Joyce's lipstick on in the mirror and taunting her, it is obvious that the make-up department forgot to put Faith's tattoo on her upper arm. It's obvious if you watch back and forth between the mirror and the shot of Faith standing and turning, there is no evidence of a tattoo that has been established Faith has in the previous season.
Continuity mistake: Near the start of 'The Wish', the scene where Cordelia is talking to the Cordettes and meets Anya. During the close-ups of Harmony, Anya is standing to camera right of the brunette Cordette behind her. A few seconds later when the shot is further away Anya is standing camera left of the Cordette.
Plot hole: In 'Graduation Day pt 2' the Mayor has his vampires stand at the bottom of the steps leading out of the school to stop any escaping students. The thing is, all the parents managed to escape out the side exits. Since the Mayor was expecting all the students to try and run too, why didn't he have these exits covered?
Continuity mistake: When Buffy receives her letter from UC Sunnydale it says her address is 1630 Crestview, this doesn't sync up continuity-wise with the episode The Body as she tells the 911 operator that her address is 1630 Revello. She didn't move so it's a definite mistake.
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Continuity mistake: When Buffy finds Dr. Gregory's glasses on the lab floor she places them on the table, from the long shot she places them at the left end of the table near a plastic tub with a white lid, with the glasses open. Then it cuts to a close up where they are in front of a book on the right side of the table and are closed. Then cut back to the long shot and they are in the original place.