Audio problem: At the start of the episode when Buffy and Dawn are with Joyce in the hospital room, Dawn starts eating jelly, and when Joyce starts speaking you can see in the left hand corner of the screen Dawn talking, but no words are coming out.
Character mistake: Willow refers to the Tunguska Blast of 1917. However, that event actually occurred in 1908.
Continuity mistake: When Buffy, Dawn and Joyce say goodbye to Doctor Kriegel after being given Joyce's medication, the position of Dawn's hair changes between shots.
Continuity mistake: In the end of the scene where they find the dead mental patient killed by the meteor alien, the group walk away from The Body leaving Riley still there, but Anya's coat can be seen in the bottom left corner after she had walked away.
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 ★