In Greek mythology, what did Perseus use Medusa’s severed head to do to the sea monster Cetus?

In Greek mythology, Perseus used Medusa’s severed head to turn the sea monster Cetus to stone. He did this while rescuing Andromeda, who had been chained to a rock as a sacrifice to the monster.

Andromeda’s mother, Cassiopeia, had claimed that her daughter was more beautiful than the Nereids. Poseidon punished the kingdom by sending a sea monster, and an oracle required Andromeda to be offered to it. Perseus arrived after killing Medusa and agreed to defeat Cetus in exchange for marrying Andromeda.

Accounts vary in how Perseus killed or immobilized Cetus. The famous version has him expose Medusa’s head, causing the creature to become stone. This use of the head is distinct from his original beheading of Medusa and from later uses against enemies such as Phineus.

Cetus is often represented in ancient and later art as a composite sea creature rather than as a zoologically precise animal.