Costello the octopus may be the first evidence of the eight-armed invertebrates dreaming, a new study says. 

Scientists at New York City's Rockefeller University arrived at their lab one morning and found the male Brazilian reef octopus with his arms wrapped inside a piece of PVC pipe, like he was trying to strangle it. The water in the tank was murky. Curious, the team reviewed camera footage from earlier that day.

What they saw surprised them: Costello appeared to emerge from sleep and then act out defensive behaviors before inking his tank.

Such abnormal movements suggested Costello was recalling “something stressful”—and possibly having nightmares, says Marcelo Magnasco, a biophysicist at Rockefeller who co-authored a