When threatened, the blue-ringed octopus can produce a powerful neurotoxin that is strong enough to kill 26 people. Fortunately, there are some physical signs that the octopus may be about to produce its toxin, including increased color intensity. Though its toxin has the power to kill multiple people, the blue-ringed octopus isn't actually responsible for many human deaths.
The neurotoxin that blue-ringed octopi produce is the same kind that is contained in blowfish, which, when served as sushi, is known as fugu. If fugu isn't prepared in the right way, it can be tainted with this neurotoxin. Improperly prepared fugu is actually responsible for more human deaths than the blue-ringed octopus.