I was most interested in the Great Hall in the Haunted Mansion:
> This is one of the most famous Disney effects of all, but the company didn’t invent the technique. In fact, the “Pepper’s Ghost” illusion is based on a term coined in the 1800s by a professor of chemistry at the London Polytechnic Institure.
> The ghosts that you see dancing and celebrating in the Grand Hall are actually animatronic figures in black rooms above and below the mezzanine that your Doom Buggy is on. There is a gigantic pane of glass between the riders and the Grand Hall. A light source shines on the animatronics below, which reflects them off of the glass and makes it appear as though they’re actually in the Grand Hall.