Christopher Nolan’s Dunkirk is a nerve-wracking movie. Three separate storylines tell the tale of the famed World War II evacuation in a intense two hours of film. A lot of that feeling has to do with how the film’s score uses Shepard tones — layered sound waves that simulate a constant ascent in tone — to create a sensation of building tension. They’re a personal favorite trick of Nolan’s: he’s based sound effects and entire soundtracks with other composers on the auditory illusion. In Dunkirk, composer Hans Zimmer crafted his soundtrack around the effect — and it’s an auditory masterpiece.