Do spiders dream?

She soon found they experience periods of rapid retinal movement, which increased in duration and frequency throughout the night, lasting about 77 seconds and happening approximately every 20 minutes. It was during these REM-like periods that Rößler observed uncoordinated body movements—their abdomens wiggled, their legs curled or uncurled.

… and

“Occasionally, there are things happening that I can only explain with the theory of them having a nightmare,” Rößler says. They’ll be peacefully dangling, legs curled by in neatly, when suddenly “all the legs get extended at the same time, like aah!”

National Geographic : Do spiders dream? A new study suggest they do.