Is it morally acceptable to eat intelligent animals? Everyone can make their own mind up about this. Some people think that there’s nothing wrong with eating any kind of animal. For me, I drew a somewhat arbitrary zoological line in the sand and decided that any animal “above” a fish was off-limits. In other words, birds and mammals are off the menu, whereas fish and invertebrates are OK to eat.

For the most part, this has served me pretty well. As Nirvana frontman Kurt Cobain put it, “it’s okay to eat fish, cause they don’t have any feelings.” And I didn’t mind eating prawns from a welfare or intelligence point of view.

But there was a problem: cephalopods. Octopus and squid are invertebrates, so following my “rule” they were perfectly acceptable for me to eat. However, their lack of a skeleton does not mean they lack intelligence — far from it. Octopus and squid — and cuttlefish, which are also cephalopods — are some of the most intelligent of all animals, and that includes dolphins, crows and apes. I brushed these concerns under the carpet and carried on eating them.

My will was put to the test when I stayed at a camp site on Hachijojima, an island in the Izu chain, almost 300 kilometers south of Tokyo. I went snorkeling with a Japanese fisherman and he caught a large octopus. He carried a large metal spike and used it to prise the animal out from a small cave.

Once we got back to shore he drove the spike into the octopus’ head and mashed its brain. To my surprise, the animal didn’t seem to die. Two of its tentacles wrapped around my arm up to my shoulder. My fisherman friend had to unpop the octopus from me. I didn’t know at the time that a significant part of an octopus’ nervous system is located outside of the brain, in the “shoulders” at the top of each tentacle. So destroying the brain does not immediately immobilize the animal.

The fisherman then set about scrubbing the top membrane from the skin of the animal and, while most of it was still wriggling around, he cut the octopus up and offered me some.

This was obviously a test of my resolve. I’d made the decision that it was OK to eat octopus, and here was one to eat. Did it matter that the animal was still clinging to me? If by my rules octopus was acceptable, it would be hypocritical to say no. I took a piece of tentacle from the knife and chewed. It was incredibly chewy and not at all pleasant.

Since then I’ve learned more about cephalopod intelligence and my misgivings about eating them have hardened. (Incidentally, I learned that the suction cups on octopus tentacles can detect a wide range of chemicals — when it was stuck to my arm, that octopus was literally tasting me.)

Octopus and cuttlefish have the highest ratio of brain to body mass of any invertebrate. Some octopuses can navigate mazes and use tools — clear signs of high intelligence. Their brains have evolved on a different track to those of vertebrates, so represent a different kind of intelligence.

Shuichi Shigeno, a Japanese biologist based in the Italian city of Naples, suggested in a paper published this year that the cephalopod neural system may form the basis for developing strong artificial general intelligence. Meanwhile, Noriyosi Sato from Nagasaki University has found that pygmy squid use ink for predation — the cloudy ink confuses prey — as well as defense.

All cephalopods are masters of mimicry and disguise, but I would like to end by focusing on cuttlefish, because they are arguably the most neglected of this extraordinary group of animals.

Kohei Okamoto at the University of the Ryukyus in Okinawa keeps pharaoh cuttlefish in his lab. One day he noticed an unusual behavior. The cuttlefish had raised their front tentacles and bent their rear tentacles as if they were jointed. The animals were moving in an odd manner, and changed color. They were mimicking hermit crabs!

But why? They could have been acting that way to avoid being eaten, but mindful of species that use ink to conceal their attack, Okamoto conducted a few experiments. His team found that cuttlefish appeared to mimic hermit crabs when small fish were present. Perhaps they were attempting to trick the fish into thinking there were no predators nearby? Crabs are filter-feeders and scavengers, and therefore pose no threat to fish. But the cuttlefish also behaved in a similar crab-like manner when they were introduced into a larger tank for the first time.

The cuttlefish were behaving like crabs, to be on the safe side. Just in case there were any predators around in the new space they were entering, the cuttlefish mimicked an unpalatable species. It’s just another example of the extraordinary intelligence of this group of animals.

And talking of unpalatable species, the more I’ve learned about the intricacies of cephalopod behavior, the less I’m inclined to eat them. These days, octopus and squid are pretty much off the menu.

Natural Selections covers issues related to scientific research in Japan on the fourth Saturday of the month. Rowan Hooper is the news editor of New Scientist magazine. Follow him on Twitter @rowhoop.

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