Kahless and Molor is an epic Klingon opera; the prelude is over two hours long. Bombastic and atonal, it is known as a classic of the genre as it conjured images of large, ferocious beasts trapped in the vast machinery of something equal parts pipe organ and refinery. It also had the added thrill of real battle sounds intermingled with the duel singers' guttural crescendos.
Deanna Troi used sections of Kahless and Molor to prevent captured Tezwan General Gyero Minza from sleeping or resting peacefully in an attempt to break him for information. (TNG novel: A Time to Heal)