In the exterior shot of the school after Buffy and Faith kill Kakistos, it's a shot used previously in Bewitched, Bothered and Bewildered (1998). You can see one of the Cordettes wearing her red jacket and red hat from the scene where they were ignoring Cordy.
The name Kakistos is Greek. Giles states that it means "the worst of the worst," but it simply means "the worst".
Buffy and Giles are walking. Giles holds a mug. He then looks at his wrist and says what time it is. Yet, the sleeve of his shirt is covering his wristwatch almost entirely.
When Buffy and Faith break the hotel window to escape Kakaistos and his followers, both of them put their hands on the broken windowsill as they leap out of the room, yet neither of them sustain wounds that scraping across broken glass would cause.
At the Bronze, immediately after Giles and Willow talks about magic, the singer's mouth is out of sync with the soundtrack.
At 29:34 the scene cuts to a hallway at Sunnydale High, and as the camera tracks a student coming down the stairs there is a moment when you can see over the top of the set at the far end of the corridor.