At one week of age, the blue ringed octopus will begin to eat crab pieces. As the octopus matures, it will begin to eat live crabs and bivalve mollusks. The octopus will either entice its prey into its vicinity and inject a poison into the water that will paralyze it or will inject the poison into its prey directly. It is also believed that the octopus will capture prey, forming an airtight pouch around it, and inserting the poison into the pouch, cause the prey to take the poison in through its respiratory system. The poison is a neurotoxin which causes paralysis, which is particularly fatal if the poison affects either the heart or repiratory system. To date there is no antitoxin. Generally though, humans are not considered prey to this creature and a bite from one seems to be more of a defensive response than anything else.
References: Boyle 1987. Microsoft 1993. Loadsman and Thompson 2000. Park 1987. Berry 1998.