Not many humans have died from the venom of the species of blue-ringed octopuses in the genus Hapalochlaena despite them living in tide pools from Japan to Australia, but all of the deaths had to be memorable.
Because Hapalochlaena venom only paralyzes voluntary muscles. The problem is that breathing is voluntary. Your diaphragm is voluntary. You probably won't know you got bit. You won't be able to signal for help. You will be fully conscious as you die of asphyxiation.
It is a tiny octopus, about the size of a golf ball, and evolution sometimes gives things that might otherwise be near the bottom of the food chain an unreal defense hack; in this case a tetrodotoxin to deter predators. Their tetrodotoxin happens to be 1,100 times more toxic to humans than cyanide, and one golf-ball-sized critter has enough venom to kill 25 people.
It's on social media so it must be legit.
There is no antivenom but you can survive; by being bit but knowing it within a minute and being a short enough distance of a hospital with a ventilator that you can have it breathe for you while the toxin metabolizes out naturally over the course of a day.
Acclaimed author Michael Crichton used a blue-ringed octopus as an assassination weapon, by eco-terrorists of course, in his novel State Of Fear.
