When the flashing blue, and not a flashing red, becomes a dire warning signal - Meet the blue-ringed octopus

Hell hath no fury like a woman scorned, or an angry blue-ringed octopus. They do give a final warning shot – a brilliant flash of blue. Within 1/3 of a second, they turn bright yellow, with each of the 50-60 rings on its body flashing a bright iridescent blue.