In 1894, a notorious Italian mystic pretended to sprout a third arm. French physiologist Charles Richet sought to identify the ethereal matter that formed it. He dubbed the idiosyncratic material—which he said didn’t resemble a solid, liquid, or gas—ectoplasm, and posited it might be what ghosts were made of. Paranormal investigators seized on the concept:
Some described a shiny, billowing ether while others theorized a viscous goo. Skeptics have caught phony mediums using gauze to simulate the substance.