Where The Wild Things Are - S4-E18
Visible crew/equipment: While the house is becoming "Wild", Riley takes Graham down to The Initiative. Once the door closes behind them and the mirror returns to its original position, the shadow of a camera is reflected in the mirror. It's in the middle of the frame, on the left, over a book case.
Where The Wild Things Are - S4-E18
Visible crew/equipment: After Anya has rescued Xander from drowning, they venture through the vines to the room that Buffy and Riley are in. The moment before Anya screams, "Xander, help me," a vine attacks her, but a crew member's hand can be seen (in the wide-screen version) moving the vine towards Anya.
Where The Wild Things Are - S4-E18
Visible crew/equipment: When Xander and Anya pull over in the ice-cream van, the front windscreen is very reflective. To avoid reflecting the camera crew, a giant screen was put in front of the ice-cream van - which, ironically, is reflected in the windscreen. It isn't a reflection of another vehicle parked in front of them as the thing that is reflected is a curved shape.
Where The Wild Things Are - S4-E18
Visible crew/equipment: In the scene where Xander and Anya make the last attempt to rescue Buffy and Riley, Anya is attacked by some vines and you can see another set of hands from the crew pushing the vine towards her.
Where The Wild Things Are - S4-E18
Visible crew/equipment: Toward the end of the episode Giles, Tara and Willow contact the spirits. Just after the spirits vanish, in the bottom left corner of the screen a crew member's leg is visible.
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 ★