The tiny blue-ringed octopus can pack a wallop. It is widely regarded as one of the world's most venomous animals. It lives in tidal regions ranging from Australia to Japan and is frequently encountered by people wading in tide pools. If provoked or stepped on, it will bite. Blue-ringed octopus poison has no antivenom and can kill an adult human within minutes.
The name comes from the bright iridescent blue rings that show up when the octopus becomes alarmed, reports MarineBio. The blue rings are a warning when threatened. If a predator doesn't leave, the octopus attacks by ejecting venom that causes paralysis, and then death. The more common blue-ringed octopus, Hapalochlaena maculosa, carries enough poison to kill 26 adults in just a few minutes.