Revealing mistake: In the opening of the season 6 episode "Two To Go", Willow has gone crazy and is trying to kill the two remaining members of the Trio, so she is pulling the brick wall of the jail apart brick by brick. The problem is that if you look carefully, they are obviously not bricks being pulled away; they look more like plastic or plaster.
Continuity mistake: In the musical episode, 'Once More, With Feeling', when Buffy is singing her song in the Bronze, 'Something to Sing About', she breaks a pool cue over a demon's head. She holds the remains in her right hand and clubs another demon in the face with it, then the camera cuts to another angle and it's in her left hand when she stabs the next demon with it.
Continuity mistake: At the beginning of the episode when the Potentials are fighting the ubervamps, when they see the second one they move away from it. You can see in the bottom right hand corner of the screen that the ubervamp already has a Potential. In the next shot you see it jump down and grab a Potential.
Visible crew/equipment: When Xander is leaning over the hole in the cemetery into which Buffy and Dawn have fallen, he causes the edge of the hole to collapse. Seen from below, everything is fine, but the shot from above Xander shows a hand grabbing hold of the back of his trousers and his briefs are visible.Janet Carter
Continuity mistake: In the scene where we see Buffy's mum drop her off at school, when Buffy is worrying that her dad will not show up, we firstly see Joyce's seatbelt is on. We then see her again and it is still on. However after the shot goes back from Buffy to herself, we can see her seatbelt is off. Then when the shot comes back to her again it is back on.
Other mistake: In the final scene, where Spike drives down the road while singing 'My Way' he turns the steering wheel significantly, but in the external shots the car is travelling down a straight road, with no bends. He is turning it sharply to the right as the camera cuts to outside, but the car continues straight ahead.
Continuity mistake: In the season 4 episode "Doomed," during the fight at the Hellmouth, Willow throws the sack of bones to Spike, who catches them and looks startled. In the very next shot of Buffy fighting one of the demons, Spike can be seen in the upper left corner of the screen, with empty hands, quite calmly watching the fight. (00:36:35)