Herbert is also known for his "variation" songs, which consist either of a series of refrains displaying different styles, or of several variations of the same melody. For example, "Serenades of All Nations" from "The Fortune Teller" demonstrates serenades from colourful national traditions, sung and danced by a ballerina. "The Song of the Poet" from "Babes in Toyland" provides variations on the lullaby "Rock-a-bye Baby" by presenting it first as a brassy march, then in Neapolitan style, and finally as a cakewalk. The best of Herbert's operetta music is challenging, calling for trained singers. He often wrote his operettas with a particular singer in mind. During his career he had occasion to work with three great prima donnas: Alice Nielsen, Fritzi Scheff, and Emma Trentini. For them, he wrote leading parts in "The Fortune Teller" and "The Singing Girl" (Nielsen), "Babette", "Mlle. Modiste", "The Prima Donna" and "Mlle Rosita" (Scheff), and "Naughty Marietta" (Trentini). He would also write shows for popular comedians of the day or noted producers. Some of these were spectacular successes ("The Red Mill", written for the comedy team of David C. Montgomery and Fred Stone, was Herbert's most financially successful show.), while others were dismal failures ("When Sweet Sixteen", written for Joe Weber, who pulled out of the production, which lasted only twelve performances on Broadway.).