The blue-ringed octopus is shy and likes to hide under rocks, only coming out at night to move around and forage for food. If it encounters danger, it will emit a dazzling blue light to warn the other side. Blue ring octopus is a very small octopus species, arm spanning no more than 15 centimeters. The blue-ringed octopus mainly inhabits the Pacific Ocean waters between Japan and Australia.

The toxicity of the blue-ringed octopus can be shown by its own color. Its skin contains color cells that can change color at will, and by contracting or stretching and changing the size of the different color cells, the blue-ringed octopus's entire appearance changes. So when the blue-ringed octopus moves through different environments, it can use the same protective color as the environment color. If it is threatened, the blue rings on their bodies flash, giving the blue-ringed octopus its name. The cells in these blue rings are densely packed with brilliant, colorful crystals formed by reflected light. Blue-ringed octopuses use these unique rings to warn other creatures that they have a deadly weapon themselves.

Blue-ringed octopuses do not actively attack humans unless they are greatly threatened. Most attacks on humans occur when the blue-ringed octopus is lifted from the water or stepped on. Another cephalopod, the flame squid, makes a similar toxin to the blue-ringed octopus.