Beneath the portico of Santa Maria in Cosmedin there is the enormous face of a Triton, which came from a fountain. Its large mouth was thought in the Middle Ages to be the mouth of an oracle, but it was mainly used for submitting liars to the judgment of God. Forced to put their hand into the orifice, the innocent escaped unharmed while the guilty lost their hand. It is said that the judges may have "helped" God to pass judgment when they were convinced that the accused was guilty.
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Cache is not in the wall. It is a small magnetic canister