Revealing mistake: When Spike is playing with the Buffybot in his crypt and has her throw him onto his bed to stake him, the shot of him landing on the bed and the Buffybot climbing on top him is portrayed by stunt doubles. The shot is then interwoven with another shot of the actual actors. But it's very obvious due to the poor editing.
Continuity mistake: In the scene where Willow and Tara are at the old High School looking for Riley, Willow uses magic to light up the hallway. Tara then asks Willow how she did it. As Willow tells her that she taught her, she tucks her hair behind her right ear. Then after Tara says, "I taught you teeny Tinker Bell light", Willow's hair is hanging back down over her right ear.
Revealing mistake: When Buffy is walking alone into the desert, a man's legs are visible in the upper-right corner of the frame and remain visible for a second or two. (00:03:35)
Continuity mistake: In the last episode of Season 5 we see Spike thrown off the tower by Doc. Spike somehow manages to change from black trousers and boots into blue jeans and white shoes mid-air. He's back in black by the time he hits the ground. (00:35:45)
Continuity mistake: In the season five episode Triangle, Anya says she has never driven before, but in Graduation Day part one she tells Xander she has her car right outside. (00:22:50)
Continuity mistake: After they finish dinner, Joyce says to Buffy that she'll have to get used to her not being around anymore because it gets so quiet. After she says this, her plate disappears.
Continuity mistake: When Riley is dressing Buffy's wound, it is much further to her left side than where she was actually staked, which was more central on her stomach. (00:00:35 - 00:02:40)
Tough Love - S5-E19
Continuity mistake: In season 5, 'Tough Love', Glory crushes Tara's hand causing her blood to drip onto the bench. In later shots however, there is no blood on the bench, it is clean. (00:25:40)
Visible crew/equipment: When Willow and Tara are talking about Dawn, just as Willow turns around from hanging her picture to say "help?", a boom mike drops in from the top of the screen. (00:18:35)
Continuity mistake: Huge continuity gaffe. When Anya and Xander see Spike and the robot in the graveyard it is nightime. Xander goes back to speak to Spike almost immediately and sees Glory's followers kidnapping him. He wakes goes back to Buffy's house and from there they, again almost immediately, go looking for Glory's house - and it is the broadest of broad daylight. You could see it was still night before they left through the windows of the house. It also begs the question of how they got Spike from Glory's house back to his crypt in the sunlight since they had no blanket. (00:26:20 - 00:28:50)
The Weight Of The World - S5-E21
Continuity mistake: When Glory is griping about human emotion, her arms change between wide shots and closeups. (00:23:00)
Continuity mistake: When Buffy, Willow, and Dawn are discussing Riley's problems in the bedroom, Dawn's hair shifts from over her shoulder in the long shots to behind her shoulder in the closeups. (00:16:45)
Visible crew/equipment: In the episode "Into The Woods" at the very end you see shots of Buffy and Riley from both the helicopter and the ground. The 2nd shot of the helicopter you can see a camera in the top right corner of the chopper. (00:40:35)
Checkpoint - S5-E12
Continuity mistake: In the series 5 episode 'Checkpoint' when Buffy has just accidently axed the dummy, watch her blindfold. It goes from being pushed up above her forehead on her hair, to being right down by her eyes. This changes between every shot. (00:27:55)
Audio problem: When Joyce is about to leave for the pre-show, we hear Xander say "Have fun, but not too much fun", but his lips never move.
Continuity mistake: The morning after Buffy is bitten by Dracula, her house address can be seen as "1313" instead of "1630."
Continuity mistake: When Buffy comes in to talk to her mum about the CAT scan, we hear her shut the door behind her. We then cut to a shot of Buffy, and can see the door slightly ajar in the background. (00:10:30)
Visible crew/equipment: When the knights start advancing in the bottom right corner of the screen you can see a crew member wearing a red plaid shirt just standing there.
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 ★