Note: First published in 1960 coll Einsteinův mozek.

Synopsis: Semper, a Roman mariner tied to the mast while the crew has ears plugged by wax as they pass the feared region of Sirens, hears them mumbling thinking aloud about the coming mutiny led his philosopher slave who also disbelieves in Sirens and persuaded him to take the shortcut route. Semper is saved by his mistress who argues with Sirens' wishes and turns the superstitious crew against the slave as he denies their existence. She explains to Semper that she heard him: "I don't believe in Sirens either. But in fear of them I believe."