The blue-lined octopus may be small, growing to at most 15 cm, but it can be deadly: its venom can cause breathing failure in humans as well as other animals. Turtles can accidentally consume the octopus when grazing and drown due to the immobilizing toxins. The blue coloring serves as a warning since it only appears when the octopus is aggravated. Even though the blue lined octopus is more likely to flee from humans than to fight, if people try to pick it up it can be quite dangerous. Therefore, if you see blue, it’s time to shoo.