Stallion heart

The dosh khaleen priestesses in the Dothraki holy city of Vaes Dothrak officiate a special ceremony when a khaleesi is expecting a child. The pregnant khaleesi must consume an entire raw stallion heart, accompanied by chanting from the dosh khaleen as they read the meaning of numerous omens. If the pregnant khaleesi is able to consume the entire stallion's heart, it means the Khal's unborn child will be strong. It is a negative omen if the pregnant khaleesi fails to consume the entire raw heart, or retches any of it up (made all the more difficult because a pregnant woman's stomach is more sensitive than under normal circumstances).

After Daenerys Targaryen learns that she is pregnant with Khal Drogo's child, she must go through the heart-eating ceremony. While for a moment she almost vomits it back up, she manages to regain control of herself and finish the entire stallion's heart. Having succeeded, the dosh khaleen proclaim that her child is a son who will be the Stallion Who Mounts the World. Triumphant, albeit smeared with raw horse blood, Daenerys proclaims that a young prince rides inside of her, and she will name him "Rhaego" - combining the names of her dead older brother Prince Rhaegar Targaryen (the last great champion of House Targaryen), and of her husband Drogo.