Continuity mistake: In the season one episode 'I Will Remember You' when Buffy and Angel are talking in the sewer Buffy's hair goes from being just a few strands over her shoulder to having a whole side over it, and back again. (00:11:05)
Visible crew/equipment: When Angel kneels down to the fridge a camera lens is visible in the top left. (00:15:21)
Continuity mistake: When Angel and Buffy are sitting down talking about their kiss, Buffy picks up a coffee mug and holds it with both her hands. But in a wide shot shortly afterwards, she is no longer holding the mug and it has moved further down the table.
Answer: Everybody including Angel saw her. After helping them and then being left alone to talk to Angel, Cordelia says that the Powers That Be let her come back one more time to help them. After Angel gets a call saying that she died, he realises that it was her spirit that was helping them the entire time.