Their blue-rings are only shown when they are agitated, they show them as a warning to keep away. Naturally everyone stays away – they may be small by their venom is lethal. If they bit you then you have about 2mins to live which is not promising if you are 20m down on a dive! There is no anti-venom and, despite their small size, it is thought that they can carry enough venom to kill 26 adult humans within minutes. Wow!