The term 'SOUND OF MUSIC EXTRAS' can be summarized as a group of nuns, which is represented by the four letter word 'NUNS'. The 1965 musical film 'The Sound of Music' featured a large cast of nuns, who were portrayed by members of the Vienna Boys' Choir. The nuns were an integral part of the story, as they provided a home for the Von Trapp family and helped them escape from Nazi-occupied Austria.