Heavily armed and maybe smarter than you

If you think an octopus is just a set of tentacles and an ink sac you are so, so wrong. And perhaps dead, depending on which body of water you may be in.

Check out these freaky facts about the world's cephalopods.

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They open jars... from the inside.

The giant Pacific octopus can solve mazes in lab tests, and, yes, it can open jars, from the inside and the outside.

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They have detachable penises

The argonaut is a different kind of octopus. When the male is in the mood for love, it throws a modified arm of sperm at its mate, the better to literally reach the much-larger female.

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They'll kill you dead

Blue-ringed octopuses deliver painless bites of paralyzing, deadly venom. Even humans aren't safe. The striking creatures are so good at what they do they're counted among the deadliest animals in the sea.

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They can predict the future

They're really good at predicting the outcome of soccer matches, or so some sports lovers think. Messi (pictured) and Paul II are just two octopuses whose supposed prognostication skills have been hailed by European fans.

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They've got their own agenda

A just-published book on octopuses, "Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness," praises the creatures for "hav[ing] their own ideas."

Some are "shy," some are "confident" and some are "particularly feisty."

"This is probably the closest we will come to meeting an intelligent alien," author Peter Godfrey-Smith concludes.

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They walk... on land

While most octopuses only experience the above-water world when we give them a hand, the Abdopus octopus can and does get around on its own -- the better to hunt crabs.

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They're capable of murder!

In South Korea, a young man was accused of murdering his girlfriend, even though he insisted she died of natural, octopus-related causes. (She choked to death after eating a live one, he said.) The man was convicted but won acquittal on appeal.

Photo by: Jung Yeon-Je/AFP/GettyImages

They know when you're eating them

Eating live octopuses is a culinary thing, especially in South Korea.

Before you dive in, though, you may want to consider that "octopuses experience the world consciously," according to one anthropologist. Or, to put it another way, when you take a bite out of a still-squirming octopus, it knows.

Photo by: Jung Yeon-Je/AFP/Getty Images

They have Vulcan blood

Should you ever lunch on a live octopus or wear a dead octopus cape, you may notice that the doomed cephalopod bleeds blue. This is because octopuses have copper (and not red-skewing iron) coursing through their system.

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This

This may not be everyone's idea of cool, but it is of note: In 2011, the Italian chef Roland Trettl crafted this piece of "eatable haute couture fashion" from seaweed and octopuses.

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They'd rather die than leave their kids

The maternal instinct to protect supersedes an octopus's own need to eat. One octo mom was observed to be on egg duty for 53 long, lonely months. When its job was done, it died. (And what noble deed have you done today?)

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They malinger

University of California, Berkeley, researchers found that when threatened, coconut octopuses "lift up six of their arms and walk backward on the other two." In that mode, they can sneak away from dicey situations faster than they can crawl.

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They make lizards look pretty lame

Sure, a lizard can regrow its tail, but asScientific American points out, that regrown tail is usually an inferior tail. Not so with an octopus' regrown tentacle. That sucker is, per the American, "basically as good as new."

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They've got nine brains

Not to be catty, but you'd need multiple ones, too, if your main one was the size of a walnut. That dig aside, octopuses are regarded as brainy sea creatures, meaning they're smart and possessed of a network of brains found in their tentacles.

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They're shifty

Octopuses are famous for their uncanny ability to blend in -- "thousands of color-changing cells" in their skin give them the ability to quickly disappear in plain sight. They share this insta-camo superpower with squid and cuttlefish.

Photo by: Tarik Tinazay/AFP/Getty Images

They've got three hearts

In "Finding Dory," Hank the octopus is called out by Dory the blue-tang fish: "For a guy with three hearts, you're not very nice." In Hank's defense, his anatomy isn't designed to make him cuddly; the hearts, plural, are there to pump blood to all of his far-flung body parts.

Photo by: Walt Disney Studios Home Entertainment

They have creepy eyes

As we previously noted, octopuses have the power to take on the colors of their surroundings. But here's the funny thing: They're colorblind. Weirdly shaped pupils, however, allow them to read their environment and adjust their look accordingly.

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They seduce, then kill

It's the female octopus who does the dirty deed, strangling the male with its tentacles, according to Scientific American scientists who've witnessed disturbing scenes like this: "The female enveloped his [motionless] body with her web and carried him to what appeared to be her den."

Ick.

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They're revered in Detroit

Since 1952, when a pair of brothers (and fish-market owners) tossed an octopus onto the hockey ice before a Detroit Red Wings playoff game, Motor City sports fans have considered the cephalopod a good-luck charm.

Photo by: Jamie Sabau/Getty Images

They've made us believe in aliens

A 2015 report on the uniqueness of the octopus morphed into a 2016 meme that the mollusk was the descendant of UFOs. To be clear, octopuses are not outer-space creatures.

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