Imagineering Disney: “You’ll notice in the above diagram that the “ghosts” were on a revolving track lined up with the Doombuggies on the opposite side of what look like normal mirrors. Light reflecting off human guests would reflect off the surface of the mirrors. At the same time light shining on the hitchhikers behind the mirrors would be visible through the mirrors, allowing both ghosts and humans to be seen together. Get it? It’s like walking by a highly reflective office building and seeing yourself in the windows and seeing electric lights inside the building all at the same time.The right lighting conditions were needed to pull off the illusion. If the house lights in the room behind the mirrors were to turn on, the mirrors from the other side would look more or less like clear glass.