The blue-ringed octopus (Hapalochlaena maculosa) is a 0.3ft (10cm) cephalopod present on the reefs of the Indo-Pacific basin and known for its deadly venom. Its blue rings are aposematic signals intended to warn its predators before it bites. They become phosphorescent only under stress or threat. Its salivary venom contains a neurotoxin, called tetrodotoxin, which causes a fatal respiratory distress.