A sound clip of the word "laurel" sounds like "yanny" to some people (people who are wrong) in a new, auditory counterpart to The Dress. Already heard it? Great! Here are some more mind-bending audio clips you should listen to.
The McGurk Effect
What you'll hear: Depending on how the speaker moves their mouth, you'll hear the accompanying sound as either "ba" or "va" or "da."
How it works: These sounds are all pretty similar, so our brain uses visual cues to clarify exactly what we're hearing. If it sounds like "ba" but the person clearly looks like they're saying "va," we'll go with "va."
Same Sounds, Different Words
What you'll hear: First the word "bill," then "bale," "pail," and "mayo."
How it works: The sounds in these words are all alike, or at least sound very similar in this recording. When you see the images to go with them, your brain emphasises the sounds that match, similar to the McGurk effect. The L's in "bill" aren't that different from the "yo" in mayo, if you really think about it.
What you'll hear: This song is just a bunch of synthesized piano notes, but you'll swear you can hear the Bee Gees singing. (There was a Mariah Carey clip like this making the rounds a few years ago.)
How it works: The vocal sounds in the original clip have been converted to digital piano notes -- not just one note per syllable, but enough of them to sound a little bit like all the different sounds we hear when we listen to singing. If you've never heard Stayin' Alive, though, you might not be able to hear all the words. Listen to the original -- the video above helpfully includes a clip in the middle -- and then you'll hear the phantom words much more clearly. This also happens if you're listening to garbled audio like a train conductor calling out a stop -- if you know what the stop should be, you'll recognise the words even if your out-of-town friend can't make them out.
Choose Your Own Syllable Adventure
What you'll hear: In the clips in this video, you'll hear what sounds like the same word over and over. What word is it, though?
How it works: These tracks play one syllable from the left speaker, and a different one from the right -- at the same time. The syllables alternate, and your brain will look for patterns and try to recognise words. (The trick still works without headphones, but it's much better with them.) The sounds are ambiguous enough that there are many possibilities for what the words could be. As explained in the video, researcher Diana Deutsch has found that your perception could depend on conditions like what kind of mood you're in when you listen to the track.
What you'll hear: A sound that rises in pitch...and keeps rising...and keeps rising... and when you get to the end of the track, you can start it over from the beginning and it just keeps going.
How it works: It's like an auditory version of those infinite staircases. You're hearing multiple tones at the same time, and they go up over time -- imagine playing a piano one note at a time from the lower notes up to the higher ones. But each note is actually a collection of low and high notes. The highest ones get quieter and fade out as the lowest ones get louder, so no matter what, there are always notes in the middle that appear to be going up in pitch. Still confusing? Check out the visuals in this Vox explainer of the effect.