Kyogen is Japan's classical comic theater, and also Japan's oldest dialogue-based drama. The earliest precursors to kyogen plays are thought to be irreverent skits performed along with court dances in the Nara and Heian periods. From the early 1400s Zeami and other leaders of noh troupes brought kyogen performers under their organizational umbrella, and kyogen plays have been performed as comic interludes between noh plays from that time until today. The most popular play in the current repertory, Delicious Poison, is one of the few for which one can identify an original literary source. As in the noh drama, kyogen developed many conventions of staging. The kyogen repertory stands as medieval Japan's secular and playful counterpart to the harsh, formal social values intended to govern the lives of Japanese. The core of much kyogen humor is in parody, which deconstructs and inverts specific texts or social types and norms. Kyogen maintained its traditional repertory and functions through World War II.