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Researchers at the Cleveland Clinic have documented two distinct sleep states in octopuses, the team reported this week. During 12-hour observation sessions, the animals alternated between a calm, immobile phase and a brief, active phase marked by skin color changes and rapid arm movements.

The active phase, which lasted roughly 40 seconds at a time, occurred at regular intervals every 30 to 40 minutes. The researchers note the pattern is structurally similar to REM sleep observed in mammals and birds, raising questions about the evolutionary origins of dreaming.

Here is a sentence I never expected to type: octopuses appear to dream. Researchers at the Cleveland Clinic watched them sleep (yes, sleep) and found two phases, including one with twitching arms and rippling skin color that looks an awful lot like REM.

I think about this every time someone confidently asserts what other animals can or can't feel. The longer we look, the smarter and stranger the rest of life on Earth turns out to be. Maybe the question isn't whether octopuses dream. Maybe it's why we were ever so sure they didn't.

In the half-lit tank, the octopus is still. Its skin, which moments ago shimmered through a dozen subtle colors, has gone slate gray and quiet. The arms (eight of them, normally restless, always exploring) are folded into the curve of the rock.

And then, without warning: a wave of pink rolls across the body. A leg twitches. A second leg follows. For forty seconds the creature flickers like a candle in wind. Then it stills again. Cleveland Clinic researchers watching the tank that night were the first to suspect, and later to confirm, what was happening — that an octopus, in its own way, was dreaming.