The tiny animal known as the hydra is the closest thing we've seen to an immortal being. They don't have a lot of organs, and the ones they have stay young because the cells are completely replenished regularly. Cut it in half, and it doesn't die -rather it reproduces. Put it in a blender and separate all its cells? It will just reform itself! The secret is stem cells, which the hydra has plenty of. -via Aeon