Listen for cascading glissandi. In musical terminology, a glissando is a continuous slide upward or downward between two notes. A police siren is an example of a glissando. Though only cascading glissandi have been recorded in the field, a unicorn's soaring glissando is theoretically possible. A glissando can sound like: an otherworldly halo a liquescent mystery a blurred leap a siren's song an eerie keening The musical notation for a glissando.