Ovoviviparous snakes give birth to live young instead of laying eggs. This differs from viviparous birth in that ovoviviparity means the eggs while not layed in a nest are retained in the body of the mother and develop there until they hatch inside the mother and then the living off spring emerge. In viviparous birth the embryo goes through the complete development process inside the mother and attached to a placenta. Mammals give viviparous birth.