When hiding and camouflaged, the blue-ringed octopus (H. lunulata) conceals the ~60 blue rings that dot its body and arms. But when threatened, in a blink of an eye, it exposes its blue rings in a series of bright flashes, a warning intended to deter predators. Optical physicists and materials scientists are interested in these displays for a number of reasons. 

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This brief in Physics Today summarizes research from the lab of Roger Hanlon that was originally published in 2012. Lead author Lydia Mäthger is currently affiliated with Roger Williams University.

Source: How the blue-ringed octopus flashes its rings | Physics Today