The title role—"one of the most taxing and wide-ranging parts in the entire repertory"—is one of the most difficult in the soprano repertoire. It calls for great vocal control of range, flexibility, and dynamics as well as containing a wide range of emotions: conflict of personal and public life, romantic life, maternal love, friendship, jealousy, murderous intent, and resignation. The German soprano Lilli Lehmann once remarked that the singing of all three Brünnhilde roles of Wagner's opera cycle "Der Ring des Nibelungen" in one evening would be less stressful than the singing of one Norma. She also commented "When you sing Wagner, you are so carried away by the dramatic emotion, the action, and the scene that you do not have to think how to sing the words. That comes of itself. But in Bellini, you must always have a care for beauty of tone and correct emission." According to the Met Opera Archives, Lehmann said this to "Herald Tribune" critic Henry Krehbiel.