Just because you're an octopus and you've got eight perfectly good arms for brawling with doesn't mean you shouldn't also make use of any potential weapons you happen to find lying around on the seabed.
This is what scientists have found, filming aggressive stoushes between the animals at a kind of Octopus Fight Club in Jervis Bay along the southeast coast of Australia. The site, which the researchers have dubbed Octopolis, features an unusually large amount of Octopus tetricus, commonly known as either the Sydney octopus or Gloomy octopus. (Poor thing, no wonder it's getting into fights.)
"A particular group of them have started living in higher concentrations than usual, which we think is because of some peculiarities of the site where they live," said Peter Godfrey-Smith, a professor of philosophy at the City University of New York and professor of history and philosophy of science at Sydney University in Australia, in an interview with Arun Rath from NPR. "And essentially, they've had to, we think, learn to get on a little bit. They've had to learn to interact more than octopuses normally have to do."
Not that the 'getting on' looks like it's going so well. In this clip below, you can see two of the animals engaging in an all-out brawl. Godfrey-Smith calls the behaviour "boxing" and says he's even seen evidence of some animals bullying others.
"There seems to be a lot of fairly ornery behaviour which has to do with policing and guarding territory," said Godfrey-Smith.
Even more sensational is the following video, which appears to show for the first time an octopus using an object as a weapon, hurling debris from a bed of seashells. Strictly speaking, it's not hurling – the octopus is expelling water through its siphons, kind of like jet propulsion. Although in this instance, it's using the technique as a combative gesture instead of for movement.
"It would be quite significant if it's happening," said Godfrey-Smith. "In general, projectile use is pretty rare among animals."
As you can see, in addition to propelling a projectile at your octopus enemy at high speed, the manoeuvre also kicks up a lot of sand into their eyes – perfect for making a quick getaway if the fight looks like it might go south.
Godfrey-Smith presented these videos along with his and his colleagues' latest research on the Sydney octopus at the recent Behaviour 2015 conference.
Their study looks at how the animal acts as a kind of "ecosystem engineer" in its marine environment, interacting with debris for various purposes (including fighting) on the sea floor.
As far as we know, no octopuses have yet broken the first rule of Octopus Fight Club. This is most likely because they can't speak.