Anyone who considers themselves a Disney Parks fan is familiar with the spectral entities that lurk in the Haunted Mansion. These semi-transparent ghouls dance, dine, and even play organ in the classic Disneyland ride. Invented before modern holograms and other high-tech optical tricks, the Imagineers had to use a technique called Pepper's Ghost to create the realistic-looking, phantasmal beings. The Pepper's Ghost illusion has been around since the dawn of Victorian-era spiritualism, which featured a love - or perhaps obsession - for all things spooky and supernatural.