Freaky 'Rubber Hand' Illusion' Works on Octopuses, Too

"In the classic rubber hand illusion, illusion, a participant is tricked into experiencing a fake arm on the table in front of them as their own: their brain feels the tickle of a feather or other stimuli they see applied to the fake arm. (The real arm is behind a partition.) Until now, only some mammals, such as humans and mice, were known to be susceptible to this illusion."

"First the scientists placed an octopus in a water tank where it could relax on a soft substrate similar to the seafloor. Then they inserted a partition that covered one of the octopus's arms and left a fake one visible instead. It was important to make the rubber arm look like the octopus's real arm because in the human experiment, the illusion does not occur if the fake hand is shaped differently from the real human hand,"

An octopus was placed on a soft, seafloor-like substrate with one arm hidden behind a partition and a lifelike fake arm left visible. The real and fake arms were stroked simultaneously, then stimulation continued only on the fake arm after about eight seconds. Six octopuses that met test conditions reacted to stimulation of the fake arm with defensive behaviors such as escape maneuvers and body color changes. The illusion required the fake arm to resemble the real arm, paralleling shape-dependence observed in humans, and the responses imply sensory integration consistent with a sense of body ownership.

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