Continuity mistake: When Buffy puts her egg down, the position of the chain and pen she sets it down by change depending on whether the shot's from Willow's side or Buffy's. (00:08:40)
Continuity mistake: Right as Buffy gets out of the car and watches Joyce drive away, Cordelia and her friend are walking up the stairs, along with a girl in a blue shirt at the top of the stairs walking towards the school. The next shot Buffy is walking towards the stairs, Cordelia is already far away chatting with her friend and the girl is blue is back on the stairs again. (00:27:00)
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 ★