Amanda Miller sits facing an old woman in Upington, South Africa, one hand on a cylindrical probe that she holds underneath the woman’s chin. “Speak,” Miller says in the woman’s native language, N|uu, and as the words flow out, an ultrasound screen flickers with the video of a tongue in motion. Linguists are using the same technology that images fetuses to study endangered languages.

For someone who studies phonetics—the science of how sounds are perceived, articulated and organized in different languages—it is crucial for Miller to track the speaking tongue. Miller is a visiting assistant professor at Ohio State University and one of about 40 linguists worldwide who uses ultrasound. This portable technology, which became affordable to linguists around 2000, allows researchers to see the tongue as it moves in real time. It is one of the only medical scanning devices that can keep up with speech; MRIs, for example, are too slow.

Before ultrasound, linguists relied on x-rays and glue-on electronic probes. The x-rays failed because they exposed subjects to harmful radiation, whereas the probes were often inconvenient. “You can imagine if you walk into a village and say, ‘Look, people, all I want to do is blow-dry your tongue and glue things to it,’ people might be a little nervous,” says Diana Archangeli, a linguistics professor at the University of Arizona who has worked with ultrasound since 2004.

Thanks to this emerging technology, Miller and her colleagues have documented some of the fastest sounds in human speech: the click consonants present in many rare African languages. Because linguists did not know exactly how the clicks were produced, the sound was placed in a “mixed-bag” category of the International Phonetic Alphabet, a universal system that catalogues all the sounds in the world’s languages. Linguists use this alphabet to study the relation between different sounds and, through that, the origins of people and languages.

Miller has investigated more than 40 different kinds of click consonants. Her research, published in 2009, organized the clicks based on attributes such as airstream (where the air comes from), place (where the mouth constricts) and manner of articulation. These changes have allowed the clicks to be properly classified into the alphabet. “Once you have the [clicks’ classifications and] subclassifications, you can begin to see similarities ... to other sounds in English, for example,” Miller says. Both “t” and “k” share some characteristics of click consonants.

Elsewhere, other linguists are using ultrasound to teach foreign languages and help the deaf to speak. As for Miller, she will continue to study endangered languages, seeking to integrate new sounds into the International Phonetic Alphabet.