Continuity mistake: When Willow hands Giles the pages she stole from the books of ascension, initially the folded side faces to the left, with loose edges of pages to the right, then in the next shot the folded edge is now on the right. (00:36:25)
Continuity mistake: After Buffy slams the Gavrok spider thing on the ground with her back, she gets pulled up by Angel. We see this shot from the back, and we see that the Gavrok is no longer on the floor or on her jacket. In the very next shot, we see Angel kick it across the floor. Where did it come from?
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 ★