Like humans, octopuses can fall for the rubber hand illusion and believe that a fake arm is theirs. This suggests they have a sense of their own body, just as we do.

The rubber hand illusion is a bizarre multisensory trick where people start believing a fake hand is their own. It involves hiding a person's real hand behind a screen and placing a fake one in front of them on a table, and then stroking both simultaneously. Watching the rubber hand being stroked at the same time as the real hand is enough to trick the brain into adopting it as its own.

The illusion was first demonstrated by Matthew Botvinick and Jonathan Cohen in 1998, and it was later shown that monkeys and mice also fall for the same trick.

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Examples of responses of octopuses in the illusion condition and the posture-incongruence condition. Credit: Current Biology (2025). DOI: 10.1016/j.cub.2025.05.017

Octopuses feel it too

In this new research, which is described in Current Biology, Sumire Kawashima and Yuzuru Ikeda of the University of Ryukyus in Okinawa, Japan, placed plain-body octopuses (Callistoctopus aspilosomatis) in a tank. A fake arm made of a soft gel attached to an opaque partition was placed over an octopus's arm so it couldn't see it.

Then both the real and fake arm were stroked with plastic calipers at the same time. After approximately eight seconds, one of the researchers squeezed the dummy arm with a pair of tweezers. The eight-limbed mollusk exhibited a defense response as if it had felt its real arm being pinched. The scientists repeated this with five other octopuses, and all showed defensive responses, such as fleeing, changing color, or retracting their arms.

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Abstract. Credit: Current Biology (2025). DOI: 10.1016/j.cub.2025.05.017

In experiments where real and fake arms were stroked out of sync, or there was no stroking or the fake arm didn't match the real arm, the illusion disappeared.

The research shows that even invertebrates, whose brains are vastly different from ours, also possess a sense of body ownership similar to humans. Studying these creatures could therefore tell us more about this key component of self-perception.

"These findings in the octopus, which has a complex nervous system that has developed independently of vertebrates, may be an important model for studying the evolution of the sense of body ownership," wrote the researchers.

Wider significance

But there are many other potential applications too. Insights into multisensory integration and self-perception could help with the development of more sophisticated robots and artificial intelligence systems. Additionally, the research may help improve our understanding of neurological disorders affecting body ownership in humans, such as asomatognosia, where a person loses awareness of one or more of their body parts.

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Edited by Gaby Clark, reviewed by Andrew Zinin