In Book Three of the Masnavi, Jalaluddin Rumi uses the metaphor of an earthen jug to illustrate how to discern a person's true inner state, particularly regarding hypocrisy. Drawing upon the Quranic principle that hypocrites can be recognized by the 'tone of their speech' (Quran 47:30), Rumi compares the act of listening to a person speak with a buyer tapping a ceramic jug before a purchase. Just as a cracked jug produces a distinctly altered or discordant ring when struck, a hypocrite's hidden flaws and insincerity are involuntarily betrayed by the tone and cadence of their voice. This analogy emphasizes that while outward physical appearances can be deceiving, the acoustic qualities of speech serve as a reliable touchstone for authenticating inner character.