One of the best-known myths of bestiality is that of Leda and the swan. One day, Leda, the daughter of King Thestios, was sleeping by the River Eurotas.
Suddenly, a pure white swan descended upon her. As he entered between her thighs, he announced that he was Zeus, the god of light, who had come to offer her two sons who would shine brilliantly in the night sky. Some time later, Leda gave birth to two eggs.
From the one came Polydeuces (who is also known as Pollux) and Helen; from the other came Castor and Clytemnestra. To this day, the twin sons Polydeuces and Castor shine as the constellation Gemini.
