How many heads does the monster Scylla have?

Scylla has six heads in Greek mythology. In Homer's Odyssey, she is a deadly sea monster living opposite the whirlpool Charybdis in a narrow strait. Each of her six long necks ends in a dog-like head, and each head is capable of seizing a sailor from a passing ship.

Circe warns Odysseus that he must sail close to Scylla because turning toward Charybdis could destroy the entire ship. Odysseus follows this advice, but Scylla snatches six of his crewmen from the deck and devours them. The six sailors taken by Scylla are sometimes confused with the monster's six heads, but the matching numbers come directly from the episode.

Later artistic and literary traditions give Scylla different appearances, including a beautiful woman whose lower body becomes monstrous and serpentine. The famous phrase “between Scylla and Charybdis” comes from this story and describes being trapped between two dangerous choices. The monster is also associated with the Strait of Messina between Italy and Sicily.