There are four distinct species of blue-ringed octopus (Hapalochlaena) that can be found in the Indian and Pacific Oceans. When threatened, they are capable of quickly changing pigmentation to display bright blue rings on their skin. They are among the most venomous creatures on the planet. A single bite from a blue-ringed octopus can deliver enough venom to kill more than 25 adult humans. Their muscle-paralyzing venom is completely painless, and the majority of victims are unaware of the attack. Read more in our post, Scuba Diving the Weird and Wonderful Waters of Lembeh Indonesia.