Odysseus blocked his men’s ears with wax, but he asked his men to tie him to the mast as he listened to the Sirens’ song. Circe warned Odysseus about the Clashing Rocks, a pair of rocks that clashed together whenever a ship passed through. Choosing to avoid that fate, Odysseus had to choose a route between Charybdis, a monster whirlpool that swallows everything near it, or Scylla, a six-headed monster that snatches people from up a fog-concealed cavern. If they went close to Charybdis, the entire ship would go down.