Once might be bad timing, an unlucky brush with death. But when the bullets keep coming, on different days and in different places, the question changes: Why does this keep happening? You start to look a little further back for answers. Bad luck starts to look more like a bad pattern.

A bad pattern was exactly what kept getting soldiers in the U.S. Army nearly killed, according to Major Kevin “Kit” Parker. Parker is a professor of bioengineering and applied physics at Harvard University, but two decades ago he was just a Southern boy who’d decided to join the army partway through graduate school, completing basic training in 1992 and getting commissioned as an officer in 1994.

“Military service is a little bit more common in my family or in the neck of the woods where I’m from—so, you know, if you watch NASCAR and you’re very susceptible to good advertising, you might find yourself in the army,” Parker says, with a laugh.

After joining the Army Reserves, Parker ended up serving two tours of duty in Afghanistan, from 2002 to 2003 and in 2009, and twice in 2011 as part of a special science advisory mission called the gray team. The 2009 tour was particularly rough, a seven-month stretch when Parker’s unit just couldn’t seem to duck the militants. Wherever they went, their convoys kept getting pinned down by gunfire.

“It was a very rough combat tour; I was getting shot at quite a bit,” Parker said. “One day I was out with some Afghan national police and we were on this kind of desert plain that was on the other side of a mountain. There was no vegetation, nothing—and I’m looking at my shirt, this . . . bluish-green pixelated pattern, and I’m looking at the dirt around me and I thought, Ί stick out like a sore thumb here!’”

The problem was the camouflage on their uniforms. Known as Universal Camouflage Pattern, or UCP, it was rolled out in 2004 to the tune of $5 billion after several years of development. Blue, green, and pixelated, the design was meant to be an all-terrain garment that would eliminate the need for multiple uniforms. But instead of letting them blend in to all environments, this one-shade-fits-all suit made the army major and his fellow soldiers stand out against what was often a barren, rocky landscape.

“This was a budget-driven decision, rather than a science-driven decision,” Parker said.

There was a combat cameraman on the day that Parker looked around his blue-suited body and had his horrible realization. The cameraman took a photo of Parker down on one knee—an image that would serve as inspiration when he arrived back home.

“All I had to do was kind of look back at my photographs from the war and I see that picture of me out on one knee out in the desert,” Parker said. “It’s like slightly less conspicuous than if I’d been holding a big sign over my head in Pashtun that said, ‘Shoot me.’”

Parker wasn’t the only one with this problem. The camouflage was making soldiers in Afghanistan easy targets—and in 2009 the issue finally reached the ears of now-deceased U.S. Rep. John Murtha (D, Pennsylvania), who reportedly heard from noncommissioned officer Rangers while on a visit to Fort Benning, Georgia. Study after study began to come out showing that UCP was a sub-par camouflage. One report in particular, conducted by U.S. Army Natick Soldier Research, Development and Engineering Center, showed that four other camouflage patterns performed 16 percent to 36 percent better than UCP across the test’s woodland, desert, and urban settings. At least one of those, known as MultiCam, had been available since 2002—which means a $5 billion expense on the research and development of these uniforms could have been avoided.

According to news reports, the issue wasn’t just the colors, or the pixelation (a technique used by several more successful camouflage patterns). The problem was also the pattern’s scale. It was too small, and suffered from a phenomenon known as “isoluminance,” where a pattern’s colors are so close together that they blend when seen from a distance and make the entire form stand out. In the case of UCP’s light-toned colors, the soldiers’ outlines became light-colored silhouettes, making them easy to see against the background. In other words, it could be making the soldiers more visible and thus, less safe.

While the cuttlefish may not be as recognized as its eight-armed cousins, it rivals them in a number of aspects, including its intelligence and its incredible shape-shifting, shade-shifting skin. The animal can change its coloration in about 300 milliseconds. Hu wanted to partner up with a marine biologist named Roger Hanlon, a researcher at the Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts, and a leading expert in cephalopod behavior (the group that includes cuttlefish, squid, octopuses, and nautiluses). And Parker realized that Hanlon’s office just happened to be nearby.

“I said, you know what? I’m right here. I’m going to walk over there and get this guy,” Parker said. The three scientists teamed up with several other colleagues and went on to publish a 2014 paper on the nanoscale color-changing mechanisms within cuttlefish skin.

Parker happened to be visiting the Marine Biological Laboratory’s library when he got Hu’s call—a library near whose doorway hangs the somewhat ironic inscription, STUDY NATURE, NOT BOOKS. It was said by Louis Agassiz, a groundbreaking biologist who helped inspire the creation of the MBL. It’s one of Hanlon’s favorite quotes. He cites it often, in joking defense of his research habits.

“Certainly that’s my excuse to get out in the world and go diving a lot,” Hanlon says.

That’s something of an understatement. Over his roughly thirty-five-year career, the biologist has performed around five thousand scuba dives, everywhere from Australia to South Africa and the Caribbean. (Among his favorite spots: Palau Islands of Micronesia and Little Cayman Island.) But back in the lab, he has a whole slew of captive cuttlefish whose stealth and smarts he and his colleagues can study on a daily basis.

I’m sitting in his office in Woods Hole, Massachusetts, at the Marine Biological Laboratory, one of the research stations hanging along the cape, just down the street from the dock that takes summer vacationers to the island known as Martha’s Vineyard. It’s a cold, clear, and quiet day in December, and the light has a thin, golden touch as it hits the enclosed harbor known as Eel Pond. Hanlon’s office looks out onto the water, a tiger-striped Nautilus pompilius shell on the windowsill punctuating the view. Books on his shelves have a certain theme: Vision and Art: The Biology of Seeing; Neurotechnology; Butterflies; and a beast of a book with the no-nonsense title, Disruptive Pattern Material stamped across its double-wide spine.

“An interesting book,” Hanlon notes, when I point it out. “That guy made a fortune off of clothing.”

Hanlon is a sort of Renaissance man of marine camouflage, but for the most part he studies all manner of cephalopods—various species of squid, octopus, and cuttlefish. When I ask him which his favorite is, he laughs, almost surprised. “The European cuttlefish is pretty phenomenal,” he says. “The one we have in our lab here. I’ve worked a lot on them; it’s a really neat animal.”

In the United States, the cuttlefish has long been the lesser-known cousin of the octopus. They inhabit the coasts off of Europe, Asia, Australia, and Africa, but somehow seem to skirt the Americas. Like their squid cousins, they have eight arms and two tentacles. Aristotle admired their iridescent innards; during his time, the animals were prized for their ink, which they spew out just as the octopus and squid do in order to throw up a defensive curtain and escape. They’ve long been called the “chameleons of the sea,” for their ability to blend in to their surroundings.

“These animals also escape detection by a very extraordinary, chameleonlike power of changing their colour,” Charles Darwin wrote in his seminal 1860 book The Voyage of the Beagle.

You may not be able to think of a weirder, more otherworldly creature than the cuttlefish. It has no backbone, strange W-shaped pupils in its bulbous eyes and thick floppy-looking arms protruding from its face. It swims around with a tutu-like frill that floats around its body, but propels itself backward to escape predators. To look at its many-fingered face is to look into the visage of Cthulhu, that fictional god of H. P. Lovecraft’s strange horror stories, or the alien Ood of the rebooted cult TV show Doctor Who.

If you think there’s little similarity between a human and a tuna fish, consider this: at least they both have backbones. As a member of the cephalopods, the cuttlefish is from an even more distant branch of the family tree than true fishes. Cephalopods, an extremely mobile group of animals that includes fellow shade-shifters like the octopus and the squid, are thought to be the brainiest group of invertebrates on the planet.

The modern cephalopod lineage first emerged more than five hundred million years ago, before even sharks had come to be. They arose from animals known as mollusks—a group whose living members include the humble snail and the clam, which is essentially a muscle armored with a shell.

How did the very clever cuttlefish evolve from an extended family that even today includes such, well, brainless creatures? The answer may lie in the shell—or the lack thereof, as it were. Mollusks were defined by their protective, calcium-rich armor—the word “mollusk” comes from the Latin molluscus, meaning “thin-shelled.” But while a shell can act as highly effective defense for vulnerable flesh, it can also be a burden—and at some point in their evolution, cephalopods abandoned their external shells, becoming highly mobile hunters and foragers in the ocean. Unlike the squid and the octopus, the cuttlefish does have a flat and oval internal shell called a cuttlebone, which is full of layered chambers. The front chambers are filled with gas and the rear chambers are filled with seawater; and by adjusting the ratio of gas to liquid, the cuttlefish can change the density of the cuttlebone—and thus, its floatability—as it swims around at different depths. That’s a big energy saver if you’re trying to move around and stay afloat. (Cuttlefish also save energy by living a quiet life, often lying on the seafloor and using their arms to toss sand over their bodies so that they’re hidden from sight.)

The trade-off to not having a shell is that you become a very tempting target for every other predator in the ocean. You’re basically a fluid bag of meat. A prepackaged, protein-filled snack. In short: you are pretty easy pickings.

Octopuses and squid, cephalopods who have also shed their shells, suffer from the same vulnerability. So these fleshy creatures have evolved an ingenious system of defense: if you can’t protect yourself when attacked, don’t draw any unwanted attention in the first place. Swim under the proverbial radar. And so they’ve developed this highly specialized camouflage that seems able, at first glance, to match nearly any color under the sea, if not the sun. It’s not a totally unique ability—animals like chameleons can also change color, depending on their mood. But few can do it with the sophistication of the cephalopods, which can not only change color but change intricate patterns that allow them to quickly blend into their surroundings, whether it’s the sandy sea-floor or a bundle of wavy kelp. They can even modify the texture of their skin to match their environment, whether it’s rough sand or a sharp-edged reef.

I get a firsthand view of this when Hanlon takes me down the hall to the lab, where the cuttlefish reside. His colleague Kendra Buresch is there in a room that sounds like an Escher sketch of running faucets—tanks full of floating cuttlefish line the far wall, and water circulates through at a high rate, as it would in an ocean environment. The animals are smaller than I expected—roughly the size of my hand—but just as cute as I thought they’d be. (It doesn’t hurt that, to my ear, “cuttlefish” sounds like “cuddlefish.”)

These guys aren’t interested in cuddling, though. As Buresch comes close, one of the animals lifts two of its arms up in the air—almost as if begging for food (though I’m told later by Hanlon that it’s a startle or threat response). They definitely have personalities, Buresch said, as she held a finger over the water. The cuttlefish focuses on her finger, and two dark, slightly wavy lines grow and thicken across the length of his back; they remind me of the twin flowing f-holes carved into a violin. The longer the cuttlefish stares at Buresch’s wiggling finger, the thicker those markings get—as if someone’s trying to fill in a narrow line with a blunt, wet sharpie, and the color is beginning to bleed outside the lines.

“So now he has a pattern on, that’s frequently the pattern they get when they’re hunting,” Buresch says. “I just don’t want him to grab me—it’s fine, I just don’t like the way it FEELS!”

Buresch’s voice rockets up two octaves at that final word, as the cuttlefish, who can stand it no more, lashes out with its two feeding tentacles and latches onto her finger. Buresch pulls back quickly and the cuttlefish releases its suckered grip, the dark lines on its back fading from front to back and quickly flickering away.

I totally want to try now. The once-fooled cuttlefish won’t be tricked again. Buresch waves her finger in front of him to make sure and he thinks about it—the lines start to draw themselves up his back, but just as quickly vanish. (They’re not in synchrony, so the effect looks somewhat like an alternating eyebrow-waggle, Stephen Colbert-style.)

So I wiggle my finger in front of his companion, who seems a little more trigger-happy. The dark lines appear, and the little guy shoots out his tentacles, hidden behind his eight-armed face, soft little suckers wrapping around my finger. It’s weird but not unpleasant, and I’m thinking about how to describe the feeling and kind of entranced by how the tentacles are shortening, making it look like the cuttlefish is reeling itself in toward my hand, and then I notice that Buresch and her colleague, Stephen Senft (who walked in about a minute before this) are making noises of significant alarm.

I pull my finger back and he doesn’t let go; I pull up, out of the water, expecting him to release—but at this point, his tentacles are so short that he just hangs on for dear life, his single-digit meal almost in reach. So I inadvertently lift him into the air. The shock (or perhaps the gravity) is finally too much for him, and he lets go and plops back down into the shallow tank.

The researchers are noticeably relieved and a little shocked. Senft says he’s played with the cuttlefish before, but has never gotten as close to having his finger become a snack as I did.

“They have a sharp little beak in there,” Senft says by way of understatement. (Its cousin, the squid, has a beak that’s measured to be among the hardest, if not the hardest, all-organic material known—which I’ll get into in the next chapter.) Meanwhile, I’m feeling pretty bad about messing with this poor cuttlefish. I ask the scientists if I traumatized the little guy.

“He’ll be okay,” Buresch says.

Animals that rely on camouflage often make use of pigment molecules that absorb most wavelengths of light and reflect only a tiny slice of the visible spectrum. This works well for most animals with yellows and reds and brown/blacks in their coats (particularly mammals, whose pigments are limited by what their hair can produce). The iridescent shades and blue greens like those you’ll see in the blazing sapphire of a peacock feather are thanks to structural color—building a nanoscale surface that does not absorb light but reflects incoming wavelengths into the blue-green range.

Some animals, like chameleons, can actively change colors at will. Those that can’t alter their appearance on command instead feature large-scale patterns—alar...