Female sand tiger shark wombs are battlegrounds for unborn sharks. Pregnant sand tiger sharks carry embryos from different fathers, and the different embryos cannibalize each other inside the womb until only the biggest and strongest remains. This winning embryo will then be born! This occurrence is known as intrauterine cannibalism. Researchers think this competition inside the womb continues the reproductive battle for the father sharks, so no further damage is done to the female shark during violent mating.