Blue-ringed octopus are famed for being one of the most venomous animals on the planet, and the symptoms from a bite are the stuff of nightmares. But how worried do you need to be?

Take this as a sign to stay away. The warning system of the blue-ringed octopus doesn’t seem to work on a lot of people, since many have taken too close a look, and been horribly bitten by its ...