The internet quickly broke into factions: some heard "Yanny" without fail, others couldn't help but hear "Laurel." In the Curiosity office, many of us started by hearing "Yanny," but after a few repetitions, the audio morphed into the unmistakable sound of "Laurel." Others could only hear "Yanny" in the original recording, but only "Laurel" when it was pitched up 40 percent. What's going on here? How can one audio clip sound so different to so many people?

There are many ways that sounds can fool you. The mere suggestion that a clip of audio might sound like something else is enough to make you hear it that way — it's why people hear messages in music played backward and why this video makes you hear "Bill" then "pail" then "mayo" just by changing the pictures you see. It also explains a freaky phenomenon known as the McGurk Effect, where audio of someone saying "ba" overlaid with video of them saying "fa" sounds exactly like they're saying "fa."

This is all because of the special way your brain processes speech — "top down," as a 2006 study in the journal Hearing Research describes it. You don't hear a sound and then analyze the frequencies to determine that it's a word that sounds like "Bill"; instead, your brain first recognizes the sound as speech, then uses context clues to decipher its meaning.

So that's step one: you were primed to hear either "Yanny" or "Laurel," and your brain got ready to hear one or the other.

Step two gets a little stranger. You've probably seen those optical illusions where a vase is also two faces in profile, or a portrait of a young woman is also a portrait of an old woman. These are called ambiguous images, and they work because they exploit the peculiar Venn-diagram overlaps in the way your visual system interprets the world. The same goes for this audio clip.

For one thing, the clip isn't perfect. As University of Texas professor Bharath Chandrasekaran told The Verge, "It's a little bit noisy, so that itself causes perception to be a little more ambiguous. Because it's noisy, your brain is filling in with what it thinks it should be."

But there's also some physics at play. Every sound is made up of a specific combination of frequencies. Those frequencies create a sort of fingerprint for the sound — it's why an A on a violin sounds different than an A on a clarinet. Your brain interprets each sound's fingerprint to determine the character of the sound you're hearing.

When you put the Yanny/Laurel clip through software that analyzes the sound, a few different frequencies pop out. (I'm a musician, so I used musical transcription software. For a more nitty-gritty analysis of the frequencies at play, check out this article by a linguist in the Atlantic.) Below is the first and second syllable of the word.

I recorded my own voice saying "Laurel" and then "Yanny," and analyzed those frequencies. There are some striking similarities.

And just to prove that these frequencies aren't common to all words, here's the analysis of me saying three other women's names: Rachel, Eva, and Allie. Allie had the closest match, but not by much.

In the same way you could see a vase or two faces in the exact same image, the words "Laurel" and "Yanny" overlap harmonically in such a precise way that you could hear either one in the same audio. Of course, the two don't have identical frequencies, which is why listening on your phone's tinny speaker versus your computer audio system (or with old versus young ears) might tip the balance in favor of one or the other.

As with every illusion, whether it's audio or visual, the peculiar way your brain can be tricked is a stark reminder that you don't perceive the world perfectly. Your perceptions are shaped by context, and your brain just does its best to keep up.

Want more illusions? Check out "The Ultimate Book of Optical Illusions" by Al Seckel. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.