Listen to one end of a phone conversation, and you’ll probably hear a rattle of ah’s, um’s and mm-hm’s. Our speech is brimming with these fillers, yet linguistic researchers haven’t paid much attention to them until now. New research by Mark Dingemanse and colleagues at the Max Planck Institute for Psycholinguistics, in Nijmegen, the Netherlands, has uncovered a surprisingly important role for an interjection long dismissed as one of language’s second-class citizens: the humble huh?, a sort of voiced question mark slipped in when you don’t understand something. In fact, they’ve found, huh? is a “universal word,” the first studied by modern linguists.

Dingemanse’s team analyzed recordings of people speaking ten different languages, including Spanish, Chinese and Icelandic, as well as indigenous languages from Ecuador, Australia and Ghana. Not only did all of the languages have a word intended to initiate a quick clarification, but its form always resembled huh? The utterance, they argue, isn’t a mere grunt of stupefaction but a remarkable linguistic invention.

In each of the languages investigated, the vowel is produced with a relatively relaxed tongue (never a vowel that requires you to lift your tongue, like “ee,” or pull the tongue back, like “oo”). And if any sound comes before the vowel, it is either an “h” sound or what’s called a glottal stop, a consonant sound formed by a complete closure of the glottis, the thin space between the vocal folds. (You use a glottal stop between the two parts of “uh oh” or the two syllables of “better,” if you say it with an extreme cockney accent.)

It’s not unusual, of course, for languages to have words or sounds in common: The English “number” and Spanish numero, for instance, share a Latin ancestor. And languages may adopt words from other languages (which is how words such as the slang OK spread widely). But it’s a basic linguistic principle that when there is no shared origin or word swapping, the word for a given thing will be arbitrarily different in different languages: So there’s “house” in English, maison (French), fángzi (Chinese) and huan (Lao).

Huh? appears to be anything but arbitrary. Dingemanse’s team has already confirmed the similarities with speech transcripts from 21 additional languages, many of them unrelated. Are the researchers sure that huh? will turn up in every language in the world? “No,” Dingemanse says. “But we are ready to place bets.”

What makes huh a word—and not, alternatively, the equivalent of a yelp? A laugh, cry or growl, however meaningful, isn’t considered language; even a dog communicates sadness with a whimper. A true word is learned, and follows certain linguistic rules, depending on the language spoken. Huh? fits this definition: For one thing, huh has no counterpart in the animal kingdom; for another, unlike innate vocalizations, children don’t use it until they start speaking. Moreover, in Russian, which doesn’t have an “h” sound, huh? sounds more like ah? In languages using a falling intonation for questions, like Icelandic, huh? also falls. All in all, Dingemanse concludes that huh? is a bona fide word with a specific purpose “crucial to our everyday language.”

But why would huh? sound similar in every language? To explain that, Dingemanse draws on evolutionary theory, saying the word is the result of “selective pressures in its conversational environment.” In a sense, huh? is such a highly efficient utterance for serving its particular narrow function that it has emerged in different languages independently again and again—what’s known as convergent evolution, or the appearance of a feature in different, often unrelated organisms presumably because it works so well. Sharks and dolphins, Dinge­manse says, “arrived at the same body plan not because they share certain genes, but because they share an environment.”

The dynamic, often fraught environment of human conversation, in which grave misunderstanding or a hurt feeling or an embarrassing gaffe is never more than a syllable away, calls for a word that instantly signals a need for clarification, is as brief as possible and is easy to produce, without complicated tongue coordination or lip movement. Without much planning—no searching one’s memory for the “right” word—a listener can interject a sleek, streamlined, wonderfully unambiguous word to keep the dialogue going. Huh?

Other interjections probably play a similar role, greasing the wheels of conversation, and they too may turn out to be universal. We won’t know for sure until linguists take a listen.

What we do know is that huh? has a rightful place in dialogue. And it has the added virtue of being nonthreatening. In that sense it definitely beats what?