At The Haunted Mansion, the rotating busts which seem to turn and follow your movements are stationary. They're not actual busts, but rather inverted mask type devices. The nose of the "bust" is actually the furthest point from the observer, not the closest. They are illuminated from behind. Since most people never expect to see anything so bizarre as an inside-out face, the brain interprets the illusion as a normal face which "follows" them as they move.
In the ballroom scene, the ghosts which appear to be dancing, dueling, etc. are not holograms or any high-tech effect. There are animatronics above and below the riders in the Doom Buggys and the ghosts are the reflections of these animatronics on a giant pane of glass.
Both of these techniques pre-date Disney.
I'm sure most have heard that the ceiling of the stretching room at MK rises, while at Disneyland in Anaheim the floor lowers. At DLR, the entrance to the Haunted Mansion is in front of the railroad tracks and the ride building is behind them, so the floor needs to lower so guests can pass under the tracks.
Jim
