Other mistake: When everyone is looking for Bobby, Matthew Lillard says that it is no use shouting because the glass is 100% sound proof. Yet when he is trapped in the cage, he hears Maggie screaming directions for him to dodge the ghost - not sound proof at all then.
Phoebe
16th Oct 2003
Thirteen Ghosts (2001)
15th Oct 2003
Buffy The Vampire Slayer (1997)
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.