What have eight legs, hunt among a group of fish and can throw a mean sucker punch?

According to research published in Ecologylast week, the answer would be octopuses (yes, octopuses, not octopi—we asked).

Octopuses punch fish. Deliberately. Sometimes there's a reason, but other times, there's no discernible excuse. Researchers caught this behavior on video.

The first time researcher Eduardo Sampaio witnessed this phenomenon, he laughed. Normally that'd be fine but at the time he was underwater wearing scuba equipment.

"I almost choked on my regulator," he said in an interview with NPR's Morning Edition. "When I saw it for the first time, I just burst out laughing."

The octopus is typically a solitary creature, but sometimes an octopus might take part in a hunting party made up of fishes. A grouper's gestures, for example, can clue an octopus into the location of prey. Sampaio and his co-researchers were studying this mutually beneficial behavior when they came across an octopus punching fish while hunting.

Although researchers have observed octopuses punching fish before, the behavior happening in the context of a hunting party is new. And it can come suddenly, out of nowhere, Sampaio said.

"You can see there some punches are almost like a small boop," Sampaio said. "And the other ones that even the whole arm curls up and uncurls afterwards, you know, like the motion of a boxer doing a punch."

The punches are fairly rare, so it's not so easy to observe, he said. The research prompts many questions he said, like "Is there a species that the octopus prefers to punch?"

In some cases, the researchers were able to determine the reason the underwater bully decided to strike.

Sometimes it's a partner-control mechanism, Sampaio explained, to drive the fish away from the octopus' next meal. Or it can be to control where the fish is swimming. Or it can be a form of punishment, he said.

And sometimes the eight-legged creature just punches the fish — with no discernible incentive.

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