What makes a musical note sound "satanic"? Black Sabbath’s eerie 1970 debut opens with the tritone—a dissonant interval once shunned by medieval choirs and later embraced by the heavy metal genre. This so-called “devil’s interval” spans three whole tones and consists of just two notes. Add a third, and you get the infamous “devil’s chord,” featured in this video. But why has it made listeners so uncomfortable throughout history? To learn more about the science, history, and musical theory behind