In the years he has spent looking after the National Zoo’s cassowary, Eric Slovak has never found himself on the receiving end of one of her assaults. That’s impressive, because she's an uncommonly monstrous creature.

Imagine an ostrich as described by H.P. Lovecraft, or maybe a turkey fused with a velociraptor. Weighing in at close to 150 pounds, she stands on powerful reptilian legs that let her stretch to six feet tall when she needs her full height. Though flightless, the cassowary is covered in a coat of long black feathers, against which her brilliant blue visage—crowned by a towering, keratinous casque—stands out like a symbol in a dream.

The feature she and her kind are best known for, however, is not her plumage. It’s her toenails: On each three-toed foot, one nail is longer than the rest. At five inches, it’s probably the closest thing you’ll find in nature to a railway spike. It isn’t particularly sharp, but it is deadly.

“If I come running at you at 100 miles per hour with a butter knife, it’s going to go right into you,” Slovak, the bird’s genial and tattooed primary keeper, tells me. When threatened, cassowaries can lash out with blinding speed, nail first. Those kicks can disembowel humans and other animals in an instant, earning the elusive, rainforest-dwelling species a reputation not just as a dangerous bird, but as the single most dangerous bird on the planet.

That might explain the black-and-yellow warning placard on the door of the cassowary pen at the National Zoo that reads: “Caution: Aggressive bird. Do not enter without a keeper present.”

Such signs are just one part of a complex array of precautionary security protocols which together have ensured that for decades no human, including Slovak, has entered her pen while she was out and about in it. Cautious and defensive creatures, cassowaries rarely attack without provocation. But the best way to avoid provoking them is to keep your distance. Accordingly, when Slovak or others visit her, they’re always separated by fences and walls.

Recently, I sat with him and an assistant while they passed chunks of large chunks of fruit—which she would snap up in her beak and swallow whole—through a small porthole in one such barrier. Safe as we were, there was no ignoring her fascinating menace.

Even when another cassowary lived in the enclosure next door, the zoo kept the two apart. They could see each other primarily through a heavily reinforced windows in their respective sheds. A personable emu named Darwin resides there now, and the two sometimes sleep next to each other, despite the fence that divides them. Yet while they seem to enjoy each other’s company, the cassowary sometimes takes a swing at the window. When she does, the whole building shakes.

“I don’t know why she does it,” he told me recently. “I’ve seen her kick the trees in her yard too. Maybe it’s just to test her weapon.”

Where the cassowary is concerned, separation and intimacy might be paradoxically entwined. Because he can never get too close, Slovak says he’s learned to observe her even more closely than he might another bird—and come to know her unusually well in the process. Of course, Sara Hallager, the zoo’s curator of birds, adds that the keepers have a relationship with “every bird out here, except perhaps the flamingoes.”* But not many other birds are six-foot-tall murdermachines.

Few are better positioned to speak to the cassowary’s temperament than Hallager, who looked after her when she first arrived at the zoo in the early ‘90s. Back then the bird wasn't quite newly hatched, but still very young and far smaller than she is now. Hallager shows me a photo taken in the spring of 1992, one that shows her looming over a small mound of feathers. “She was a sweet little bird,” Hallager says. “She would sit in my lap, and she liked to be petted.”

Cassowaries are almost adorable when they’re young, their brown feathers sometimes striped like watermelons. They don’t take on their more monstrous appearance until they grow large and powerful enough to defend themselves. One day, before her adult coloring had come in, Hallager noticed that her charge’s companionable nature had begun to change. “I remember going in, and she displayed the first sense that she was a cassowary. She kicked. She didn’t kick me, but she kicked at me,” Hallager recalls. At that point, she went to her then-supervisor and said, “Okay, I think we need to stop going in with her.”

While the cassowary has mellowed in the 20-odd years since, neither Hallager nor her fellow keepers have violated that dictum. Today, when they want to weigh her, they rely on a scale hidden under the straw and sand in her shed, studying its readings remotely. Medical inspections take place from afar: Even when the animal is trying to hide its illness, “you kind of know when your bird is off,” Slovak explains.

While it can be strange to call the veterinarian on what amounts to an intuition, Hallager adds, everyone involved understands that it’s the right approach. “Because the keeper knows the bird so well, the vet knows that’s an accurate reading of that animal,” she says.

At feeding time, Slovak and his keepers speak to the bird in high pitched voices, much as you might your cat or dog. She even has a variety of "pet" names: Hallager has long called her Earlina, in deference to a confused child who once pointed at the two cassowaries and, presumably confused about their gender, announced, “That’s Earl!” Over the years, other keepers have sometimes referred to her as Apples, largely to differentiate her from the the zoo’s other cassowary, who disliked the fruit. After that bird moved to another zoo, Slovak started simply calling her "Cassowary." But when he says it, you can hear the capital letter—and you can tell he’s speaking to and of this bird.

Yet even those who know the zoo’s cassowary best still sometimes find her strange. Slovak has gradually trained her over the years, so that she now sometimes comes when he calls (though her keepers try not to make her do anything against her will). But that doesn’t mean that she’s domesticated, he says. Hallager agrees. Even though she was born in captivity, this strange bird “still has that mysterious aura about her—that prehistoric, dinosaur-walking-through-the-rainforest-quality," she says.

The dinosaur comparison is familiar for those who admire cassowaries. In her book Birdology, naturalist Sy Montgomery devotes an entire chapter to the topic, arguing that cassowaries help illuminate the reptilian ancestry of all avian species. Yet these birds are mere evolutionary holdouts; they adapted to their own environments long ago. Accordingly, they’re actually further from us than the ancient beasts they resemble—a fact that makes the connections they forge with their keepers that much more remarkable.

That bond seemingly goes both ways. Though it’s been years since Hallager was a daily presence in the cassowary's life, she believes the bird knows her, recognizes her. “I feel like she needs and wants that interaction,” she says. According to Slovak, there are concrete signs of this mutual recognition. Sometimes, when he or Hallager approach, Earlina will crouch down in her brooding pose, much as she might for a male while preparing to breed.

Peculiar as such behavior seems, it’s likely a partial consequence of the fact that she’s long been deprived of contact with other members of her species. But that fact is soon to change. In the year and a half prior to my visit, Slovak and his colleagues have been gradually preparing to send Earlina to a zoo in San Antonio. There, in accordance with the larger cassowary species survival plan, she’ll be partnered with a male bird that Slovak already optimistically describes as “her boyfriend.”

Preparing Earlina for that trip has been a slow and arduous process. Cassowaries are known for their caution; the last two syllables of their name, Slovak jokes, are accidentally apt. After studying how other zoos accomplished similar transitions, he has been gradually crate training her. He first enticed her to stand on a wooden platform, where she would “do the hokey pokey,” putting one foot on to snatch food and then dancing back. As she grew more comfortable, he added one wall, then another, then a roof and a rear door.

Hallager feels that Earlina’s departure is necessary, since it’s important to give her the chance to mate, especially as her own status has become more central to the survival of her species. “She’s never had that opportunity. I feel she deserves that,” Hallager tells me, “deserves to be a normal cassowary. She deserves to live in a warmer climate as she gets older.” And yet it’s not easy to see her go. After 27 years with Earlina, Hallager was already mourning their parting when we met.

“We know that we’re sending her to an institution where there’s a breeding male,” she says, wistfully. “But of course I’ll be sad. Of course.”

Editor's note October 7, 2016: An earlier version of this article stated that Sara Hallager was the Zoo's keeper of birds; she is the curator.