Zener cards were created in the early 1930s by psychologist Karl Zener and parapsychologist J.B. Rhine at Duke University to scientifically test extrasensory perception (ESP) under laboratory conditions. The deck consists of 25 cards featuring five simple, emotionally neutral symbols—a circle, a cross, wavy lines, a square, and a star—which allowed researchers to easily calculate a 20% baseline for random guessing. Rhine’s early publications sparked massive public fascination and drew interest from figures like Carl Jung. Today, Zener cards remain a famous pop-culture staple, famously featured in the opening scene of the 1984 movie Ghostbusters and still used by modern magicians for mentalism displays.