When Donald Trump meets with Kim Jong Un sometime in the next two months, there is a non-zero chance that the high-stakes nuclear summit descends into rounds of school-yard taunting.

Should Trump call Kim “fat” and should Kim respond by calling Trump a “dotard”—as each, remarkably, has done in the past—it will fall on their respective interpreters to deliver those broadsides in the other’s dialect. And though doing so might precipitate a nuclear holocaust, there is nothing that can be done about it. The words will be translated.

“Yes, of course,” said Dimitry Zarechnak, who served as Ronald Reagan’s interpreter during his summit with former Soviet leader Mikhail Gorbachev, when asked if Trump’s interpreter would have to tell Kim that the president called him “little Rocket man.”

The discussions surrounding a potential Trump-Kim summit is already fairly volatile.

The president agreed to the meeting on a whim. But as recently as this past Thursday, he signalled his displeasure at having to go through with it at all. “This should have been done by somebody before they were in the position that they’re in right now,” he said at a White House event.

It’s not entirely clear if Trump will, in fact, go through with it. His former top adviser, Steve Bannon, has expressed his belief that it will be logistically impossible to pull off. And the appointment of former UN Ambassador John Bolton—a man who seems more disposed to preemptively bombing North Korea then talking with its leaders—as the new national security adviser makes the likelihood of a summit even more remote.

But should it transpire, one of the more critical responsibilities will fall on the interpreters. The role that they play in presidential tete-a-tetes is often overlooked, if not entirely ignored. And for good reason. The interpreter is, at his or her most basic level, a oratorical tool for a conversation between other individuals. They are accessories, not players.

But they don’t just robotically translate words either (indeed, they scoff at being called “translators” as opposed to “interpreters”). Often, indeed, their job involves a fair amount of intuition, study, and diplomacy. Those tasks become exceptionally more difficult at a summit with world leaders. For the one set to happen between Trump and Kim, the hurdles are even higher, do to the enigmatic nature of both leaders and the existential nature of the talks.

“These are historical talks, if they happen. And the interpreter will play a huge part in this,” said Judy Jenner, a Translation/Interpreting Studies faculty member at U.C. San Diego and a member of the American Translators Association . Kim, she said, “doesn’t speak English, as far as we know.” And as for Trump, “If you know him and worked for him it would be easier. But he is a significant interpreting challenge.”

Interpreting has been around for as long as the need has existed for people to converse between languages. Jenner playfully calls it humanity’s “second oldest profession,” though the actual professionalization of the practice has an unclear history. Interpreters played vital roles in commerce, exploration, religion and scholarship dating as far back as antiquity. More modern, formalized interpreting has been witnessed in judicial settings—think, the Nuremberg trials—and diplomatic gatherings—think, Nicole Kidman’s turn as the United Nations interpreter who overheard too much in the movie aptly titled The Interpreter.

Those who practice it say interpreting is both an art and a science. It is a science in that interpreting involves the systematic study of dialect and diplomacy. The competition within the State Department to be considered a top interpreter in a prospective field is intense. It is an art in that there are unique styles and it’s not always precise. Indeed, when Trump speaks to Kim, a fair amount of editorial leeway will fall on his interpreter to communicate what exactly the president is saying.

“Any kind of translation or interpretation is the rendering of the idea from one language to another,” is how Zarechnak put it. “The term ‘literal’ or ‘word-for-word’ doesn’t mean anything because it is always subject to interpretation.”

What Zarechnak is getting at is the distinction that exist between the two main types of interpreting. There is the so-called “simultaneous” model, which is when the speaker and the interpreter talk virtually at the same time. This is the version practiced by Nicole Kidman: headset on, speaking into a transmitter that blurts out the speech in a different language to those on the other end of the line. It is cognitively, incredibly challenging.

The second kind of interpreting is “consecutive.” In this setting, the interpreter sits next to the person for whom they’re interpreting and take notes as he or she is talking. It is only when that person is done that the interpreter translates the comments into the other language.

“That is the holy grail of interpreting,” said Jenner, noting the incredible difficulties that come with mastering this craft. Interpreters must have subject matter expertise, so that they don’t get flummoxed by complex matters or provincial phrases and topics. And they must learn a special note-taking system that allows them to keep up with the conversation.

“It takes thousands of hours of practice to get to a good technique,” Jenner added. “The good ones don’t even need to take a lot of notes.”

Consecutive interpreting—which will be used when Trump meets Kim—is easiest when the speaker talks slowly and stays on script. Former President Barack Obama, Jenner said, did both. “His speech was very beautiful and he wasn’t particularly fast,” said Jenner. “He was just a great natural orator.”

Oratorically, Trump couldn’t be more different. The president rarely stays on talking points and often has a disjointed speaking style. He doesn’t make up words. But their meaning is not always readily apparent. Occasionally, he will contradict himself in a matter of moments.

“He is difficult to interpret,” said Jenner. “Usually, the clearer you are as a speaker the easier it is. If you ramble a lot, and don’t speak in full sentences, and leave thoughts hanging, it isn’t easy to interpret.”

Precisely understanding what Trump hopes to convey is one hurdle. Translating it for Kim’s interpreter is another.

Korean is the language of the North. But there are idiosyncrasies that separate it from the more commonly used version of the South. Mainly, there are fewer foreign words and influences that have made it into the dialect, owing to the country’s isolated status globally.

“I had no problem understanding them,” said Jacki Noh, a long-time interpreter who worked on the nuclear-arms-focused Six Party Talks with North Korea in 2003. “But sometimes they had a problem understanding me when I was using the South Korean words.”

Ultimately, Noh said, the language barriers should pose few, if any, problems for whoever is tasked with interpreting for Trump. And if there is enough preparation before the talks, the president’s penchant for going off script can be surmountable too.

An interpreter can, in the end, make adjustments on the fly. Zarechnak said that twice, maybe three times, in his career, he paused a translation in order to first clarify a clear error that his speaker had made. The conversation stopped, reversed course, and then started all over again. What he’s never done is deliberately soften a message because of the geopolitical horrors that could ensue upon its delivery.

“No,” said Zarechnak, “I’ve never gone rogue.”