Richie Goulding is whistling (humming? singing?) parts of Ferrando's "All'erta!" from the beginning of Giuseppe Verdi's Il Trovatore. This long melodramatic aria gets the opera off to a rousing start.
All'erta! means "On guard!" or "Be on the alert!" Ferrando, a captain of the guards in the palace of Aliaferia, sings it to his chorus of sleepy men-at-arms as he comes on stage, telling them to do their job. To wake up, they ask him to narrate the dreadful tale of their former ruler, the old Count di Luna. Ferrando obliges them, saying that they must know the former Count was blessed with two sons: the present Count di Luna and his younger brother Garzia. The latter was only a baby when his nurse awoke to find an old gypsy witch standing next to his cradle and apparently casting spells on him. Servants rushed in and seized the sorceress. She protested her innocence, saying that she was only telling the baby's horoscope. But the child sickened, and she was burned at the stake. From the pyre she demanded that her daughter Azucena avenge her death, and Azucena complied by stealing the child. Pursuing her, Ferrando and other soldiers found a fire with embers still smoking and the half-burned bones of a child: "d'un bambino—ohimè—l'ossame / Bruciato a mezzo, fumante ancor!"
This bloodcurdling story sets the soldiers on edge, and Ferrando completes the job by telling them that the old witch still haunts the area as a spirit, creeping about the roof at night and flying through the air. An old man died when she appeared before him, in the form of an owl, at the hour of midnight . . . At that moment a clock strikes twelve, and all the soldiers rush to their posts, uttering maledictions.