Coming soon to a cool movie theatre near you: Metal: A Headbanger's Journey.
On the surface there might appear to be no link between Black Sabbath, Wagner's Gotterdammerung, West Side Story and the theme tune to the Simpsons.
But all of them rely heavily on tritones, a musical interval that spans three whole tones, like the diminished fifth or augmented fourth. This interval, the gap between two notes played in succession or simultaneously, was branded Diabolus in Musica or the Devil's Interval by medieval musicians.
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(Thanks: Triple-B)