Lover's Walk - S3-E8
Other mistake: In the final scene, where Spike drives down the road while singing 'My Way' he turns the steering wheel significantly, but in the external shots the car is travelling down a straight road, with no bends. He is turning it sharply to the right as the camera cuts to outside, but the car continues straight ahead.
Other mistake: When the detective is interviewing the woman in the alley he says "So you heard the man scream about what time?", but Finch didn't scream as he died.
Other mistake: In "Doppelgangland", Vampire Willow struggles to remember Cordelia's name. However, it is still Willow, she knew Cordelia from being human (we see this in The Wish as well).
Other mistake: When we first see one of the Hellhounds at the clothes store that Cordelia works at, it jumps through the window, smashing the glass, and then attacks a customer who's wearing a tuxedo. But the Hellhound attacks the customer several seconds after it smashes through the window, giving the customer a chance to escape. But the customer just stands there unaware of the Hellhound, having not heard the window being smashed.
Other mistake: At the end the library that was rigged with explosives blows up. But the school's main entrance and the clock tower blow up as well, even though they are not rigged with explosives.
The Harsh Light Of Day - S4-E3
Other mistake: We've seen before that vampires are fine as long as they aren't in direct sunlight, yet in this episode Spike is in the shade when Buffy removes the ring and he still starts fizzling.
Other mistake: Just after Giles becomes completely blind, Spike gets up to get a book off of the mantle. When he does this you can, very briefly, see James Marsters reflected in the glass doors of the bookcase that was behind him, despite Spike being a vampire. (00:27:00)
Other mistake: In the scene where Spike escapes from a blind Giles, he pushes Giles out of the way and does not get a shock to the head from the chip in his head, which normally goes off with the most minor hint of violence.
Other mistake: Towards the end of the episode when Spike tells Buffy to stake him and removes his shirt, you can see that he has a tan on his upper back/neck to his hairline from wearing a t-shirt.
I Was Made To Love You - S5-E15
Other mistake: According to Buffy's watch, the first scene with her, Dawn and Joyce starts at 4:23 PM and ends at 4:24 PM. But the scene lasts much longer than that.
Other mistake: The newspaper that Xander is reading in the library has the same text over and over again and does not at all match the headlines. (00:18:05)
Other mistake: As Spike follows Buffy into the hallway by her front door we see Spike's reflection in the mirror. Vampires do not have reflections, so Spike should not have been visible.
Seeing Red - S6-E19
Other mistake: At the Bronze, when Warren punches Xander the first time, Warren never actually punches him, and Xander starts to go up in the air before you even hear the sound of the punch.
Other mistake: We're shown a variety of photographs and pictures of different members of the gang at one point. One of those, the one of Xander and Anya, is actually a shot from the episode "Something Blue". I doubt very much that during the events in that episode, someone conveniently decided to take a photograph.
Other mistake: When Buffy is talking about Spike's trigger she says, "He's a bomb and I need to know how to defuse him." The DVD subtitles misspell "defuse" as "diffuse." (00:23:55)
Other mistake: When Buffy pulls the knives out of the Bringers, there is no blood on them. Also, you can see the muscular arm of Buffy's stunt double pushing the knives into the Bringers. (00:34:00)
Other mistake: When Robin Wood is burying Jonathan, Jonathan's face flinches when the first heap of dirt lands on his legs.
Other mistake: When The First (disguised as Eve) tells the Turok-Han to kill everybody except Buffy, it runs past her towards the exit of the crypt. The First then says, "Well, alone again", turns to face Spike and transforms into Buffy. In this shot, the Turok-Han can be seen still leaving the crypt, even though it had plenty of time to reach the exit and was running towards it at full speed.
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 ★