Revealing mistakes: Although subtle movements by at least three of the dead bodies in Hainsley's showroom could be written off to the way they were mounted, or being buffeted by air currents, the illusion is somewhat spoiled when his manservant enters the room and the corpse closest to Angel quite clearly blinks.
Revealing mistakes: In the scene where the butler comes to kill Angel, one of the dead women behind Angel blinks.
Audio/visual unsynchronized: You could tell a large amount of Spike's lines were looped, as his mouth sometimes doesn't fit what he's saying.
Continuity: If Spike cannot touch anything at all -- this is a big point throughout the season - - how on earth can he sit in Angel's chair? And why doesn't anybody call him on it?