Video Footage: Is This Octopus Having a Nightmare?

Costello the octopus was napping while stuck to the glass of his tank at the Rockefeller University in New York. He snoozed quietly for half an hour, and then entered a more active sleep stage, his skin cycling through colors and textures used for camouflage — typical behavior for a cephalopod.

But soon things became strange.

A minute later, Costello scuttled along the glass toward his tank’s sandy bottom, curling his arms over his body. Then he spun like a writhing cyclone. Finally, Costello swooped down and clouded half of his tank with ink. As the tank’s filtration system cleared the ink, Eric Angel Ramos, a marine scientist, noticed that Costello was grasping a pipe with unusual intensity, “looking like he was trying to kill it,” he said.

“This was not a normal octopus behavior,” said Dr. Ramos, who is now at the University of Vermont. It’s not clear when or if Costello woke up during the episode, Dr. Ramos said. But afterward, Costello returned to normal, eating and later playing with his toys.

“We were completely dumbfounded,” said Marcelo O. Magnasco, a biophysicist at Rockefeller. Perhaps Costello was having a nightmare, he and a team of researchers speculated. They shared this idea and other possible explanations in a study uploaded this month to the bioRxiv website. It has yet to be formally reviewed by other scientists.

After the incident, Dr. Ramos reviewed the footage of Costello’s activity, which was recorded as part of a behavior and cognition study (the lab was also observing another octopus, Abbott; both were named after the heptapod aliens in the movie “Arrival”). In total, the team found three more shorter instances that appeared similar.

To Dr. Magnasco, the behaviors exhibited in Costello’s longest spell evoked the acting out of a dream. The curling of arms over his body looked like a defensive posture, he said. In the footage, the animal is seen perhaps trying to make himself look larger, and then he tries an evasive maneuver — inking. When he fails to escape, it seems like Costello seeks to subdue a threat by strangling the pipe, Dr. Magnasco said, adding, “This is the sequence of a fight.”

But he also acknowledged that “this is one isolated instance on an animal that had its own peculiarities.”

There are other explanations for the behavior, such as a seizure or neurological problems, which could be related to Costello having lost parts of two limbs before he was caught. But Dr. Magnasco said he hoped that, by reporting the incident, other scientists would watch out for the behavior, which his group observed by mere chance.

Tamar Gutnick, a neuroethologist at the University of Naples Federico II in Italy who wasn’t part of the study, said that the researchers needed to address questions in peer review, like one about what happened around the same time the next day. Her colleague at the same university, Michael Kuba, a marine behavior biologist, also said they needed to detail Costello’s typical sleeping behavior.

The study’s researchers said that they could account for such queries, as they have footage of the octopus’s entire life in the lab.

Another problem with interpreting this octopus’s behavior, Dr. Kuba said, is that Costello “was not completely chipper and healthy”: The animal had stomach parasites.

Dr. Kuba suggested that some of the behaviors, such as the curling of arms, might have resulted from cramps, perhaps because of a problem with Costello’s digestive system or from the parasites reaching a part of his nervous system. Similar behaviors occur in captive octopuses, and they’re usually related to stress or age, he said. Costello died about six weeks after the longest episode.

Still, the idea of dreaming in octopuses is compelling, Dr. Gutnick said. The Rockefeller team isn’t the first to propose the idea that cephalopods dream as they move through different phases of sleep. Because octopus body patterning is controlled by the brain, researchers have wondered if patterns during sleep could be responses to dreamlike replay of events.

In their own research, Dr. Kuba and Dr. Gutnick recently recorded electrical signals from an octopus’s brain. That opens the possibility that researchers could snoop on octopuses’ brain activity during sleep and maybe connect behaviors and body patterning during sleep with shifts of brainwaves to study processes linked to dreaming.

But that is not necessarily related to this observation, Dr. Gutnick said, adding, “You have to show that they have dreams before you think about nightmares.”