In this episode, Nick brings us back to the ocean to visit one of its most bizarre inhabitants, the jellyfish. Some have tentacles over 100 feet long, others have a sting that can kill a human being in under five minutes, but most fascinating of all are the ones who've achieved immortality. Then, Dave asks one of the most difficult questions in science: If a catastrophic, world-ending event was on the way, who would you choose to survive in order to repopulate the Earth and how would you save...