(in English, "the Mouth of Truth") is a renowned image, carved from Pavonazzetto marble, of a man-like face and located in the portico of the church of Santa Maria in Cosmedin in Rome, Italy. The sculpture is thought to be part of an ancient Roman fountain, or perhaps a manhole cover, portraying one of several possible pagan gods.
The most famous characteristic of the Mouth, however, is its role as a lie detector. Starting from the Middle Ages, it was believed that if one told a lie with his hand in the mouth of the sculpture, it would be bitten off. The piece was placed in the portico of the Santa Maria in Cosmedin in the 17th century.