Continuity mistake: In the episode Prophecy Girl, during Buffy's rooftop fight with the Master, her shoes change in between shots from white heels, to black boots when she's kicking him, back to white heels. (00:41:35)
Continuity mistake: When Buffy drowns in Prophecy Girl, she falls into the pool with her hair tied in a ponytail and her arms under her. When she is discovered by Angel and Xander, her arms are by her sides and her hair is loose. (00:33:55)
Continuity mistake: When Buffy falls down after the Master bites her, you can see her fall, then hear her hit the dry ground. But then a few shots later she falls again and this time into water.
Continuity mistake: When Buffy descends into the Master's lair, the way she is holding her crossbow changes depending on the camera angle. Sometimes it's pointed straight forward, sometimes it's pointed upwards.
Continuity mistake: When Giles and Jenny are talking about Buffy, Giles says "We must get in touch with this Brother Luca chap!" watch Giles. In the first shot he's still reaching towards the top of the cabinet. Instantly in the next shot, he's in the middle pulling something down from the top of the cabinet.
Continuity mistake: When Giles and Jenny are talking in the library, when Jenny closes the bible, the way she's holding it changes instantly between shots.
Continuity mistake: When Buffy is consoling Willow after she discovered the dead students, as Buffy leaves the room, Willow's mouth is open and she looks down. It then cuts to a wideshot. Instantly, Willow's mouth is closed and she's staring forward, and she looks down a second time.
Continuity mistake: When Jenny meets Giles after Xander's botched attempt at asking out Buffy, the way she's holding the folders to her chest subtly changes repeatedly between the closeup and wide shots.
Continuity mistake: When Buffy turns down Xander's date proposal at the start of the episode, throughout the scene, Xander has his backpack up around his right shoulder. However, when he walks away, it's instantly down by his side.
Continuity mistake: In the beginning, when Xander is practicing asking Buffy out with Willow, at once point Willow puts one of her snacks (candies, I think) into her mouth and starts chewing in a medium/wide profile shot of the two. It then cuts to a closeup of her and instantly she's no longer chewing, and immediately places a second candy in her mouth. She didn't have time to stop chewing and swallow between cuts.
Continuity mistake: When the earthquake happens at the start of the episode, and we see the Master celebrating, his hands instantly change positions at least twice between cuts. (Sometimes it matches perfectly between cuts other times they're in an entirely different position between cuts).
Continuity mistake: When Buffy stakes the first vampire at the beginning, in the first shot, his hands are in towards his abdomen. When the camera cuts behind him, and he falls back, suddenly they're instantly extended partially outwards to either side.
Continuity mistake: When Cordy stops kissing her boyfriend and says "What was that?" at the beginning of the episode, the lighting on Cordy's face changes completely as it cuts between the two camera angles. In the first angle, the lighting is much darker and shadowy, while in the second angle, her face is suddenly much brighter.
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 ★