Asif Ghazanfar is a neuroscientist at Princeton University. Here’s his tale from the field as told to Jessica Boddy.

For decades, neuroscientists thought nonhuman primates couldn’t speak because their hyoid bone—found near the larynx—is situated differently than ours. But that notion is based on monkey-cadaver research from the 1960s, when tools to see live voice boxes didn’t exist.

Recently, we used X-rays to record one of our lab’s macaques, Emiliano, as he ate, yawned, verbalized, and smacked his lips. With those videos, we traced his vocal anatomy frame by frame, and made a catalog of every contortion it could make. Further analysis showed he is fully capable of producing five distinct vowel noises.

Once we knew monkeys could articulate, we wanted to know how they would come across. We used a program that produces audio based on vocal structure. My colleague’s wife chose the common phrase: “Will you marry me?” The result is clear, if extraordinarily creepy: It sounds like a very small, aggressive person popping the question.

Goosebumps aside, this finding flips what we knew about primates’ ability to talk. If anatomy isn’t preventing them from speaking, what is? That’s my next challenge.

This story originally published in the Noise Winter 2019 issue of Popular Science.