Because most of Zwartjes' films are in fact silent movies, without dialogue or direct sound, the music always plays a major part. Zwartjes makes the music himself, often with his brother Rudolf and with Lodewijk de Boer. Audition (1973) is a good example of a film with a wonderful music tape. The film is a visual improvisation between the camera and the actors, almost without story line - a man looks at and listens to a woman singing, while another woman is watching the two - and with mainly intriguing black and white images. The music, too, is based on improvisations. With Christian Manders, Tineke and Moniek Toebosch.