Octopuses are like aliens on Earth: three hearts, blue blood and the ability to squeeze through a space the size of their eyeballs, but the secrets of the octopus are more extraordinary than we ever imagined.

Octopuses are like aliens on Earth: three hearts, blue blood and the ability to squeeze through a space the size of their eyeballs. But there is so much more to these weird and wonderful animals. Intelligent enough to use tools or transform their bodies to mimic other animals and even communicate with different species, the secrets of the octopus are more extraordinary than we ever imagined. "Secrets of the Octopus" will premiere in celebration of Earth Day and is the next installment of the groundbreaking, award-winning, natural history "Secrets of" franchise. The first installment was "Secret of the Whales," and the second was "Secret of the Elephants."—National Geographic