OCTOPUSES change colour when they sleep, and it might be because they are dreaming. Sidarta Ribeiro at the Federal University of Rio Grande do Norte in Natal, Brazil, and his colleagues have found that some octopuses go through two distinct stages of sleep, one active and one passive. They recorded four common octopuses (Octopus vufgaris) in the lab over day and night periods. During the day, the animals slept for more than half the time. "In quiet sleep, they stay in the same position for long periods of time - very quiet, very pale the pupils closed - and breathe regularly in a very quiet manner," he says. This was punctuated every 30 to 40 minutes by active sleep, lasting 1 to 2 minutes. In this phase, the animals showed changes in colour and texture, including the fine bumps on their skin. Their eyes and arms also moved, their suckers contracting. "It's clearly a very active state," says Ribeiro.
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