Apparently determined to prove that he would sleep with anyone or anything, the Greek God Zeus seduced the Titan Metis in his youth, prior to his marriage to Hera. In fact, he went so far as to marry her, even though she was his aunt. Metis was a patron of wisdom, and it was known that her gifts in this area would be inherited by her offspring. In fact, it was prophesised that the union of Metis and Zeus would produce a son even more powerful than Zeus himself, and to forestall this, Zeus swallowed Metis whole.
Demonstrating the importance of chewing one’s food, Metis carried her child to term inside Zeus, which caused him a terrible headache. When his head was split open to relieve the pressure, the child of Zeus and Metic, grey-eyed Athena, new patron of wisdom, burst forth fully grown and fully armoured.
It’s best not to think about the mechanics of all this too much.