Continuity mistake: When Buffy is told that Angel has become Angelus, she mentions "I should have known. When I saw him at the house he was different", but her earlier conversation with him took place not at the house but at his apartment. This isn't just a strange turn of phrase - the scene was originally shot at the Summers house, but was changed to Angel's apartment for more emotional resonance.
Reptile Boy - S2-E5
Continuity mistake: When Buffy is at the party, we see that she is wearing black shoes with a high heel. But when she is fighting Machida, the heels are considerably lower.
Continuity mistake: When Willow is interrogating Jonathan, she makes a comment about how he resented being pushed around. In the first shot, she's facing him. It then cuts to the opposite angle, and she's facing sideways. Then, in the very next shot, she suddenly turns 180 degrees between cuts after walking by him.
Continuity mistake: When Willow shows up at Oz's house to talk, her hair keeps switching back and forth between being behind her back or in front of her shoulders.
I Only Have Eyes For You - S2-E19
Continuity mistake: When George shoots Mrs. Frank, her body falls off the balcony headfirst on a closeup shot. She flips in the air once on her way down. But in the following wide shot, she flips in the air on her way down again.
Some Assembly Required - S2-E2
Continuity mistake: When Cordelia is being tied up in the corridor, Buffy leaps up, kicks the attacker, and drops to the ground next to Cordelia. In the next shot the attacker is stumbling to his feet, and Buffy is standing again, then quickly kneels down beside Cordy.
Continuity mistake: When Buffy, Willow, and Cordy are talking at the swim meet (after Gage waves at Buffy), the way Buffy is holding her hands changes back and forth between two positions as it cuts between her and Cordy. Seems two different takes were used, and she had her hands in slightly different positions in them.
Continuity mistake: When Angelus is spitting out Gage's blood, he goes from straight up to leaned over between cuts.
Continuity mistake: After Willow says that the student was killed by being opened up like an Oreo "except without the chocolaty cookie goodness," Buffy's hands go from together to apart instantly between cuts. She then puts her hands back together only for them to be apart again in the next shot.
Continuity mistake: When Buffy is talking to Cameron in his car near the start, the amount of light on Cameron's face coming through the windshield changes between cuts a few times. Sometimes the top is up over his eyes, sometimes it's down by his nose, etc. Also, depending on the angle, sometimes there's a purple glow on his face and sometimes not.
Continuity mistake: When Buffy and the guy are talking at the beach in the beginning, right before they hear a voice scream "Somebody help me!", the guy starts to turn to look at the tide. However, in the next shot, he's instantly facing Buffy again and then turns to face the tide a second time.
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 ★