Prince Xunsun once remarked: "Back when I was in the capital, I once saw a man performing illusions in the bustling marketplace. He carried a wooden box beside him, divided into twelve compartments, with a green frog in each square. He would tap the frog's head with a thin stick, causing it to croak. If someone paid him, the performer would randomly strike the frogs, as if beating a gong, producing all the notes of the pentatonic scale—gong, shang, jue, zhi, yu—each clearly discernible to the ear."