Audio problem: When Buffy is about to close the door as she goes into the bathroom, it actually never closes. But we still hear the sound of the door closing. (00:15:20)
Other mistake: When Buffy is talking about Spike's trigger she says, "He's a bomb and I need to know how to defuse him." The DVD subtitles misspell "defuse" as "diffuse." (00:23:55)
Other mistake: When Buffy pulls the knives out of the Bringers, there is no blood on them. Also, you can see the muscular arm of Buffy's stunt double pushing the knives into the Bringers. (00:34:00)
Revealing mistake: As Buffy throws Spike into a wall after he bites Andrew, Spike's stuntman is visible in-shot. His hair is slightly different to James Marsters'.
Continuity mistake: When Willow confronts Andrew outside the butcher shop, her hair changes position between shots throughout the entire scene.
Continuity mistake: When Buffy ties Spike to a chair before the opening credits, she ties a rope around his left arm three times. But two extremely fast shots later, the rope is tied around his left arm four times.
Other mistake: When Robin Wood is burying Jonathan, Jonathan's face flinches when the first heap of dirt lands on his legs.
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 ★