Other mistake: When Willow is attempting the spell in the hospital, the subtitles state that Xander is speaking a line of the incantation. It is actually Oz speaking - Xander is off rescuing Giles, as we see in the very next shot.
All The Way - S6-E6
Revealing mistake: In one fight scene, Buffy uses a car door to block a kick from a vampire. The window of the car breaks before the kick connects with it. In fact, it breaks while the foot is still in mid-air. (00:37:00)
Continuity mistake: In the scene where Buffy has just finished fighting the demons, she begins climbing up chains and if you look at her shoes, they continue to change until she reaches the ground above the chains and runs off. (00:40:30)
The Harsh Light Of Day - S4-E3
Continuity mistake: When Buffy and Spike are fighting on campus during the day, Xander tries to help Buffy but Spike throws him against a lamppost. When he lands in the ground he falls completely on the grass on his side but if you look behind Spike in the next shot he lies half on and half on the grass on his front.
Visible crew/equipment: In the scene where Willow visits Xander to discuss what may be going on with Oz; towards the end of the scene, when the camera is on Willow, you can see the sound mike at the top left of the screen next to the green crate in two different shots.
Plot hole: How did Buffy know where to find Riley at the end of 'Into The Woods'? He told her he was leaving with the army, but he never mentioned the helicopter pad. (00:40:30)
Continuity mistake: Where Willow is pulling the bricks out of the jail near the beginning of the episode. When she first pulls the bricks out of the arch thing they are from a different area than when you see the arch from the inside of the jail, even allowing it to be 'inside out' (as seen from outside and then the inside).
Continuity mistake: Ampata tells Buffy she has no lipstick, but earlier that episode we saw her using lipstick, in the high school bathroom right before the bodyguard attacked her. (00:24:20 - 00:25:40)
Continuity mistake: When Buffy is told that Angel has become Angelus, she mentions "I should have known. When I saw him at the house he was different", but her earlier conversation with him took place not at the house but at his apartment. This isn't just a strange turn of phrase - the scene was originally shot at the Summers house, but was changed to Angel's apartment for more emotional resonance.
Dead Things - S6-E13
Continuity mistake: In the episode (series six) where Buffy thinks she killed Warren's ex-girlfriend, when she's at the police station, in the over the shoulder shot of Desk Sergeant, he is holding the phone between his shoulder and ear. But in the front shot of him the phone has jumped to his hand. (00:36:45)
Reptile Boy - S2-E5
Continuity mistake: When Buffy is at the party, we see that she is wearing black shoes with a high heel. But when she is fighting Machida, the heels are considerably lower.
Get It Done - S7-E15
Continuity mistake: In the episode 'Get It Done' when Dawn and Buffy find Chloe's corpse the door across the hall from them is open. When it cuts back to them after the ad break it is shut, but there has been no time lapse.
Other mistake: In "Doppelgangland", Vampire Willow struggles to remember Cordelia's name. However, it is still Willow, she knew Cordelia from being human (we see this in The Wish as well).
Continuity mistake: After Buffy finds Dr. Gregory's glasses at the start of Miss French's class and places them on the table, they move position twice throughout the rest of the scene.
Deliberate mistake: Though vampires are said to possess super-human strength, and are in fact demonstrated to have it, they are often kept confined by the flimsiest of restraints. One distinct example is in season 2 episode 9 when Kendra locks up Angel he is unable to break out despite being held in by nothing but a flimsy padlock. This mistake is pointed out in the DVD commentary as an unavoidable 'mistake'.
School Hard - S2-E3
Plot hole: When Buffy and Sheila are walking out of school after the meeting with Snyder, Xander runs up to talk to them. He mentions during this scene how Buffy will be helping out at the Parent-Teacher Night, but he shouldn't know this - Buffy only just found out about it in the meeting with Snyder.
Other mistake: When the detective is interviewing the woman in the alley he says "So you heard the man scream about what time?", but Finch didn't scream as he died.
Answer: She has superpowers, ergo fast movement. The reason she outruns him so easily in "Touched" is that she stops trying to actually fight him and just dodges instead.
Shay