Continuity mistake: When Buffy's mom sets down the carton of orange juice on the table after the golf trip, watch closely. The continuity is nightmarish. The carton rotates multiple times between cuts. The cap is on, then off, then back on again between cuts. And Buffy's mom's hand keeps moving on and off the carton between cuts.
Continuity mistake: After the mini-golf scene, Buffy comes down to her kitchen. Her mother greets her and sets down a carton of orange juice. In the first shot, her mother is holding the carton with both hands. But in the next shot as she sets it down, she only has one hand on the carton.
Continuity mistake: When Buffy, Xander and Willow are talking at the school near the beginning in front of the vending machine, watch the way Buffy is holding her pink binder. First she's holding it to her side, but shifts it in front of her chest. Instantly, in the next shot it's back by her side. Then it's back in front of her chest again.
Revealing mistake: In the beginning of the episode, when Buffy stakes the vampire that she beats up for a long time, watch when she lifts the stake. The hole in the vampire's chest is a solid 8" below where she actually hit him with the stake. (It's an effects shot, so somehow, they just didn't line up).
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 ★