Behold a tentacled, immortal predator with a wound for a mouth. No, this isn't the product of a horror writer's fever dream, but rather a denizen of the natural world. In this episode of Stuff to Blow Your Mind, Robert and Christian consider the hydra, from its mythological namesake to all the fascinating scientific studies about its sex life, longevity and penchant for tearing itself a new mouth hole each and every mealtime.