The first time Natalie Portman speaks in Jackie, Noah Oppenheim’s arthouse semi-biopic about former first lady Jackie Kennedy Onassis, is three minutes into the movie. It’s a week after John F. Kennedy’s assassination, and a journalist from Life magazine has come to the Kennedys’ home in Hyannis Port, Massachusetts, to interview her. He offers his condolences.

Portman, a startling amalgam of cheekbones, sharp brows, and a thicket of root beer-colored hair, lets out a breathy, biting rebuke.

“Have you read what they've been writing? Krock and Merriman and all the rest?” she snaps, referring to journalists Arthur Krock and Merriman Smith. “Merriman is such a bitter man. It's been just one week and already they’re treating him like some dusty old artifact, to be shelved away. That’s no way to be remembered.”

Merely reading that line doesn’t do justice to the voice Portman adopted for the role. If you’re not aware of how Jackie Kennedy spoke, listening to Portman’s Jackie is like the tingle of soda in your throat. It often feels familiar, but in certain spots it pops and jumps. The way she lops off the end of “bitter,” the funny hop in “artifact,” the way she rolls through “remembered” — it’s like she’s invented her own unique way of speaking English:

But Portman’s delivery is accurate in the way it captures the former first lady’s affect. And that might be the most impressive element of her Oscar-nominated performance.

Jackie Kennedy will always be an American icon; her style was impossibly chic, her beauty is immortal, and her poise and grace in the aftermath of tragedy will never be forgotten. Embodying any of those characteristics onscreen is no small feat. But it’s Kennedy’s distinctive voice — a peculiar drawl that defies simple linguistic classification — that presents the greatest challenge for any actress who might attempt to imitate her.

Jackie Kennedy spoke like an old-time New Yorker … sort of

When linguists study accents and dialects, they listen for “features” that help differentiate one speaking style or characteristic from the next. In this case, the term refers to how certain words and vowels are pronounced; they are what makes certain accents stand out or sound strange if we’re not used to them. Kennedy’s accent contains several different features, but according to several linguists I spoke to for this story, the most pronounced ones are “non-rhoticity,” which is also called “R-lessness,” and a “split short A system.”

Non-rhoticity is generally heard in Northeast and Southern accents, and particularly in older people who were born before WWII, since it’s a feature they grew up with. In plain English, it’s when someone drops the “R” sound in words like “bar” and “guardian,” pronouncing them “bah” and “gahdian.” A recent pop culture example: Kevin Spacey’s Frank Underwood on the Netflix series House of Cards:

The non-rhoticity feature originated in England, whose different regional dialects display a mix of rhoticity (where people pronounced their words with R’s intact) and non-rhoticity (where people drop their R’s). When different groups of English immigrants settled in the United States in the 1800s and earlier, some brought over the non-rhotic affectation — typically to the metropolitan areas that are now Boston and New York City, as well as the South — and some brought over the rhotic affectation. For a period of time prior to WWII, non-rhoticity was also considered posh or fashionable because of its origins in Britain.

The linguists I spoke with explained that Jackie Kennedy’s accent is at least partially typical of someone with her upbringing, in that it tracks with her early childhood in Southampton in the 1930s but was clearly influenced by going to school in Manhattan and spending a lot of time there growing up.

“You don't hear some of those stereotypical New York features in her accent, but you do hear that R-lessness,” says Anne Marie Olivo-Shaw, a linguistics PhD who researched and wrote her dissertation on New York City English dialect among different ethnic groups on Long Island, New York.

Olivo-Shaw explained that there are other features heard on Long Island and in New York City like the “cawffee” vowel, and the “e” vowel. The “cawffee” vowel turns the vowel sound in the word “coffee” and similar words into more of aw-sound. The latter turns the word “me” into something closer to “may” or “mae.”

For Olivo-Shaw, the feature of Kennedy’s accent that most stood out was R-lessness.

“She says ‘the cah’ [instead of ‘the car’] and ‘fine ahts’ [instead of ‘fine arts’],” Olivo-Shaw explained.

But there are also curious wrinkles.

“I also noticed that she dropped her R’s in a place where not all New Yorkers do — it’s an extreme place to drop your R’s,” said Kara Becker, an assistant professor of linguistics at Reed College told me. Becker studies the New York City accent.

“It’s when she has an “err” sound that’s stressed in a word. So a word like ‘furniture,’ a lot of people who drop their R’s wouldn’t drop them there, but she did. So you get ‘fuhnituh.’”

The other particularly noticeable feature of Kennedy’s accent is a “split short A system.” Both Becker and Olivo-Shaw defined it as the short A vowel sound changing in words where you’d think it would be similar.

“The split short A system happens across the Northeast, but it's very specific in different regions. So in New York it happens in words like ‘bat’ versus ‘bad,’ [where ‘bad’ can sound closer to ‘bed’ if there’s a split system],” Olivo-Shaw said. "Kennedy says ‘kehnt’ instead of ‘can’t.’”

You can also hear it in the way Kennedy says the word “back.”

“We [linguists] talk about vowels in where they’re produced in the mouth,” Becker explained, noting that Kennedy has an extreme case of this. “Her tongue is in the back of her mouth when the word ‘back.’”

Try pulling your tongue into the back of your mouth and saying “back” or “pass.” It changes the A vowel sound, so that you make less of an “ack” or “ass” sound; instead, it sounds a bit rounder. If you pull your tongue forward in your mouth, and try it again, it changes the word.

Kennedy’s R-lessness and split short A system are not only regionally specific, but historically specific, because characteristics like R-lessness have slowly faded from New York accents over time. According to linguists, there was a shift around World War II where features like R-lessness started to become less pronounced. Because R-lessness isn’t as common or as conspicuous as it used to be, its presence in Kennedy’s accent can make her sound especially unusual to younger generations.

“So some people might have none of the features of New York City English, but then they might have a split short A system, which is actually pretty common,” Olivo-Shaw said. “And among the younger people, they don't have as many of the features in general as older generations do.”

Jackie Kennedy was affluent, and her wealth is reflected in the way she speaks

There’s a rule of thumb in linguistics that you tend to see a higher number of pronounced features in working-class people than affluent people. But during Kennedy’s time — from her childhood in the ’30s into her adulthood — upper-class individuals in the Northeast exhibited certain speech patterns, often taught in expensive private schools, that combined elements of British English and American English, resulting in what is sometimes called a “prestige” accent (it’s also known as Mid-Atlantic prestige accent, and colloquially as the “Boston Brahmin” or the “Locust Valley Lockjaw”) .

This accent was characterized by a distinct pronunciation that sounds like a mix between British and American English.

“People in private school, people of a certain social class, that’s the way they talked,” Rebecca Babcock, a professor at University of Texas of the Permian Basin, told me. “It has an upper class, or an upper-crust — they call it an index.”

Babcock is an expert in sociolinguistics, and cites Franklin Delano Roosevelt and John Kerry (in his earlier speeches) as examples of people who speak with this prestige index, but explains that it has also appeared in pop culture when people want to create a character who appears to be intellectual or well-to-do, like Effie Trinket in The Hunger Games and Stewie from Family Guy.

Babcock says that what stood out to her about Kennedy, in addition to the first lady’s accent, was her grammatical formality. Kennedy, whenever she appeared on television, always sounded very proper, often formalizing her language by saying “one” where most of us would say “you.”

“One has to pay attention to one’s speech to use ‘one,’” Babcock told me, emphasizing the stateliness and perhaps awkwardness of saying “one” in a two-person conversation. “The natural is to say ‘you.’ So that sort of grammar — that’s a careful use of proper grammar.”

But Babcock noted that Kennedy’s adherence to formality wasn’t consistent, and that instead of saying the phrase “going to,” which is what one would expect considering Kennedy’s fondness for proper grammar, Kennedy used the word “gonna.”

“People don’t 100 percent of the time use 100 percent of all the features of whatever dialect they’re speaking,” Babcock said. “It’s variable.”

And Becker connected some of the nuances of Kennedy’s speech, like the way she pronounces “furniture” or splits her A’s, to what she was likely taught as a child and the affluent social circles she was part of.

“One thing she does a lot is aspirate her T’s. If you have a T at the end of a word, most Americans don’t produce a puff of air, but you can. She does this a lot,” Becker said explaining that when Kennedy would say words like “can’t” and “but,” you’d hear a little breath that almost sounds like a split-second gasp or an “uh” sound.

According to Becker, aspirated T’s link Kennedy’s accent more to her affluent background than to a specific place.

Jackie Kennedy was a politician, and politicians often change their accents to match their audience

When Portman was asked how she learned Kennedy’s accent, the actress told the Los Angeles Times that she looked up every interview with Kennedy that she could find on YouTube and watched the first lady’s 1962 White House Tour over and over.

It’s important to note that Kennedy’s White House Tour, as well as much of the archival footage we have of Jackie Kennedy, first aired on broadcast TV. That means that when Kennedy was filming an interview, for example, she would have known that it’d be seen by people all across the country.

As Babcock stated above, no one speaks with 100 percent of their features 100 percent of the time. Humans change the way they speak based on the situation they’re in and who they’re speaking to; think about how some people tend to speak with more of an accent when they visit their hometowns, or the way we sometimes speak differently at work versus at home.

Theoretically, if people shift their vocal patterns based on who they’re speaking to, then a situation where Kennedy was speaking on television would no doubt shift the way she, and other first ladies and politicians, spoke. Political figures, after all, have to convince the people they’re talking to to believe in them and support them, and that’s hard to do if you sound like an outsider.

Politicians fine-tuning their speech for their audiences happens all the time. Barack Obama’s speeches have been analyzed for their cadence, and linguists have examined President Donald Trump’s speaking patterns at length.

If there’s one thing in particular that Jackie wants to convey, it’s that no one knew the power of image in politics like Jackie Kennedy. Quite simply: She knew how to present herself, and that includes how she sounded.

“Jackie's tone was very quiet, very breathy,” Babcock said (Babcock also explained that her one issue with Portman’s delivery is that she delivers it with a “creaky voice” affectation and less breath). “That is also a cultured way of speaking. And of course that was also taught because a ‘lady’ at that time would speak in a soft, cultured, and very clear way.”

Kennedy was fully aware of how important her public appearances were in terms of how she was perceived. Leaning into certain features of her accent, while mitigating others, could account for the more curious and inconsistent pockets of her speech — like the way she formalizes the “you” by saying “one” instead. And the moments when she does break with formality could be her way of trying to be appear more approachable. While we can’t know for certain how Kennedy made her grammatical choices, Babcock stressed that her public interviews were probably rehearsed backward and forward, and that Kennedy, again like many politicians, was prepped on how to appear.

The linguists I talked to all explained that Kennedy’s accent is something of a rarity today. Back then, it might have been a rarity too, unless you floated in the same upper-crust circles she did.

Today, you may be able to find older New Yorkers and New Englanders who speak with Kennedy’s soft, rolling intonation laced with the prim touches of finishing school. But it won’t be super easy. That’s why younger generations might not be familiar with what she sounded like; to many people, she’s just that glamorous first lady they read about in textbooks. And that’s part of the magic of watching Portman’s performance in Jackie — learning something new about someone we thought we knew. Capturing Kennedy’s voice was an essential part of bringing the movie to life.