Researchers filming sleeping octopuses saw bursts of skin patterns flicker across their bodies during an active sleep phase, much like the displays they use while awake.

It is too early to say an octopus dreams the way a person does. What the footage does show is that a two-stage sleep cycle evolved separately in animals that last shared an ancestor with us more than 500 million years ago.

Why it is in the vault: it is the kind of find worth coming back to. Add sources, corrections and related links in the discussion thread.