Ramkali is considered one of the most complex ragas to sing as it is perfectly symmetrical (unlike either the major or minor scale) and contains many of the notes that are most dissonant against the drone.  This arrangement asks the choir to speak what might be "percussion solos" during the raga.  Western music uses nonsense syllablkes (Do, Re, Mi...) to teach pitch and intervals; Indian music uses syllables to teach rhythmic patterns.