Johann Strauss II wrote two operas: "Die Fledermaus" ("The Bat") and "Zigeunerbaron" ("Gypsy Baron"). They are full of fun: lively music and jokes which can sometimes be made different in each performance: the singers can put in their own jokes about modern times. Sometimes they are called operettas because they are so light-hearted. They are a mixture of Hungarian and Viennese atmosphere.