Visible crew/equipment: When Buffy and Riley are talking at the crime scene, where he tells her about Maggie Walsh's death, one of the camera shots has a very visible black border around the entire edge of the screen as if the lens shade was visible in front of the lens and could be seen in the shot. (00:18:20 - 00:19:40)
Continuity mistake: When Buffy is talking to Riley, she puts the scarf on her head, on his hand. He talks to her and says "Maybe I am the bad guy," and in the next frame her scarf is back on her head again, then off again in the next frame. (00:24:20)
Visible crew/equipment: When Buffy, Willow and Anya are watching Looney Tunes, some stage lights are reflected in the globe behind Willow.
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 ★