Octopuses given the drug ecstasy become more social and try to hug each other, a new study has found.
US Researchers at Johns Hopkins University say the drug affects the creatures in a similar way to humans.
Scientists say the way they behave on the drug may give insights into how their social behaviour has evolved.
Ecstasy also known as MDMA is a powerful mood changing drug which affects the human brain with a chemical called serotonin.
Serotonin is a drug that makes people more sociable.
Gul Dolen, a neuroscientist at John Hopkins University School of Medicine who led the study, designed an experiment with three connected water chambers.
One containing a trapped octopus and the other a plastic toy.
Four other octopuses were placed inside the tank to test their response.
The researchers measured how long they spent with the other animal and how long with the toy.
They were then exposed with the liquefied version of MDMA, which they absorbed through their gills and placed in the chambers again.
The study found that all four spent more time in the area with the other octopus than they had before the drugs.
"They tended to hug the cage and put their mouth parts on the cage," Professor Dolen told the BBC.
"This is very similar to how humans react to MDMA; they touch each other frequently."
The findings suggest brain chemicals may be key to social behaviour across very different species.
However, other researchers have raised questions about the study.
Professor Harriet de Wit from the University of Chicago, who has studied how ecstasy affects animals, said it was "innovative and exciting" - but that we can't be certain the drugs were fully responsible.
Ideally, the experiment would be repeated on a larger scale, the researchers agreed.
And some of the octopuses would be placed in the tank for the first time after absorbing ecstasy, and others would not.
Prof de Wit said that would help rule out the idea that they were friendlier the second time because they'd got used to the tank, or the other octopus.
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