How does Virgil silence Charon?

In3 of
Dante's Inferno , Dante and his guide, the Roman poet Virgil, come to the
banks of the river that separates the realms of the living from Hell, which only spirits may
enter. An old man with "eyes of burning coal" is in charge of the "bark" (a
kind of boat) that takes souls across the river. His name is Charon, and he is...