Continuity mistake: After Buffy finds Morgan's brain, Willow pulls up Morgan's school file on one of the library computers without even touching the keyboard. One moment the monitor is on the desktop, the next it's showing Morgan's file.
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)
Continuity mistake: Willow is turned into a ghost. Throughout the entire episode, she can't touch anything (can't turn the pages of a book, etc.), yet towards the end when she and Giles go to Ethan's shop, and she leaves, you can hear that she opened and closed the door, even though she can walk through walls and can't actually touch the door. The curtain moves when she leaves too. (00:34:05)
End Of Days - S7-E21
Continuity mistake: Towards the end of the episode whilst Buffy is fighting Caleb with the scythe, right after he says to her, "You're not slipping out of this fight, girl. Can't you see? You can't stop me. I can just keep going back for more. It's like being reborn," and throws her into a wall, the position of the scythe changes constantly between shots.
Continuity mistake: Sunnydale apparently has docks ('Consequences' and 'Surprise') and is quite close to a beach ('Go Fish'), but when Sunnydale is destroyed in 'Chosen', we see an overhead shot of the crater and it appears to be in the middle of the desert, far from any coastline.
Continuity mistake: While Buffy is in the hospital, they zoom in on the bedside clock changing from 2:26 to 2:27. In the next shot of Buffy, you can see the clock in the background and it reads 12:15.
Continuity mistake: In the episode 'Teacher's Pet', when Ms. French is eating her bug sandwich, her sleeves go from being up in the long shots to being pulled down in the close-up of the sandwich. (00:24:05)
Welcome To The Hellmouth (1) - S1-E1
Continuity mistake: When Giles is giving his speech about the Hellmouth the books Buffy's holding keep changing from facing him to facing Buffy and back again. (00:18:20)
Continuity mistake: Buffy's birthdate starts at 1979. In "I Robot, You Jane", when the demon pulls up Buffy's file in the school system, it shows her year of birth as 1980 and her year as sophomore. But when her file comes up on the student's computer screen, it's changed to 1979 and that she is a senior. It wasn't until towards the end of season 1 in "Nightmares" that her birth year is 1981 (on her tombstone before she comes out as a vampire). (00:08:30)
Continuity mistake: Joyce is driving Buffy to school and she is wearing a pink tank top. At school that day her shirt is white, but the next day at school she is back to wearing the pink outfit. (00:15:50)
Continuity mistake: Buffy gets a massive scar on her head from fighting with Adam. This scar changes size at least twice throughout the rest of the episode.
First Date - S7-E14
Continuity mistake: When Buffy goes to save Xander from Lissa, she knocks a dagger out of her hand and it is thrown to the ground near the far end of the room. Two shots later it has moved closer to the door.
Once More, With Feeling - S6-E7
Continuity mistake: When Buffy jumps off the stage in the Bronze that Dawn and Sweet are on and starts dancing, one of Sweet's goons that is lying unconscious moves from the far left of the bottom of the stage to the far right between shots.
Continuity mistake: After Buffy decides not to take the antidote to the demon's venom, we cut to a scene at the mental institution. She says she wants to go home with her mum and dad. As she says this her dad puts his hand on Joyce's left arm. In the following shot, Joyce suddenly has her right hand on top of his when it wasn't in the previous shot.
Continuity mistake: When Oz leaves and holds Willow close to him, the position of their noses changes depending on the camera angle. In the shots of OZ they're pressed together and in the shots of Willow they're not.
Continuity mistake: When Buffy decides to leave again and goes to her room to pack, her door is three quarters shut when she goes in, half open when Willow comes in and almost fully open when Joyce comes in. At no point does anybody touch this door.
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 ★