Character mistake: When the zombies break into Buffy's house, she stakes one to check if it's a vampire. But she should know full well that it isn't a vampire as they all broke into her house without being invited.
Continuity mistake: When Willow hides under the table in the classroom after fleeing The Pack, we see that it is on legs and doesn't touch the floor. Yet when Xander comes in and scans the room, he sees the table but Willow's feet aren't visible, even though they should be judging by the height of the table from the floor.
Once More, With Feeling - S6-E7
Continuity mistake: From the start of the second scene in the Magic Box, the doughnut and cruller on Xander's plate constantly switch places. (00:03:35 - 00:05:50)
Continuity mistake: When Dawn is in Principal Woods' office to talk about the accident, she gets up and leaves. Her bag is still hanging from the chair, but she has it in the next scene.
Continuity mistake: At home Buffy helps her mother open a crate. She tears off the cover and leaves it hanging by the side. Next shot the lid is back on. Not nailed anymore of course, but there was no time to put it back on.
Beneath You - S7-E2
Revealing mistake: When Buffy throws Spike into the benches at the church you'll notice that as he is about to hit the floor there is a blue mat where he lands. (00:36:15)
Continuity mistake: In episode 'Anne', when fighting the hell dimension demons Buffy's shoes change from trainers to plain pumps in different shots.
Continuity mistake: When Buffy is fighting Kendra the fragments of the table she is thrown onto have disappeared when she stands up again. (00:42:40)
Continuity mistake: After they finish dinner, Joyce says to Buffy that she'll have to get used to her not being around anymore because it gets so quiet. After she says this, her plate disappears.
Continuity mistake: Before the gang head over to the high school basement at the beginning of the episode, Dawn's hair is straight with curly ends. But once they're in the basement her hair is suddenly curled all over.
Continuity mistake: The white outline drawn by the coroner does not match where Kendra's body fell after being killed by Drusilla.
Continuity mistake: When Pat puts on the demon mask and punches Buffy into the bedroom door, she hits the door with her back and then falls to the floor on her face. In the immediate shot she hits the floor again, but this time on her back.
Chosen answer: From what we see in the series, certain girls are identifiable as potential Slayers - Kendra clearly fell into this category. The identification method is presumably mystical in nature, but the Watchers' Council are pretty effective at that sort of thing, so they're quite good at tracking down the potentials ahead of time. Not perfect, though - it does appear that Buffy herself may have slipped through the net - certainly she had no inkling of what she was until she'd already taken on the role of Slayer. It is possible, however, that this was actually cultural - an American family would hardly be likely to turn over their daughter to some strange man for 'training', so the Watchers might have chosen to keep an eye on her covertly, whereas some other cultures (like Kendra's Jamaican parents) might be more willing to believe.
Tailkinker ★