A weird audio illusion has gone viral on TikTok and elsewhere, and it's really going to break your brain.

As the text in the video explains, you will hear some audio, but you will hear it as two different words depending on which you are reading at the time.

If you listen to the audio while reading the word "brainstorm," that is what you will hear. But if you read the phrase "green needle," you will hear that word instead.

To really confuse your brain, listen to it again and read or think of a different phrase.

So, what is happening here? Unlike the Yanny vs Laurel debacle, it's unlikely to be to do with frequency or pitch. People are able to hear both phrases depending on what they're focusing on at the time, whereas with Yanny and Laurel people were generally only able to hear one version, until the pitch of the audio was shifted.

It's more likely that this effect is a form of the McGurk effect.

The McGurk effect, shown in this video from the BBC's Horizon program, is a phenomenon where your brain can be tricked into hearing different things based on the visual information you are perceiving at the time.

In this case, you hear either "baa" or "faa" based on the way the man's mouth is moving, despite the audio never changing. What you see can override what you hear.

In terms of "brainstorm" versus "green needle," the sound information is simply overridden not by what you're seeing at the time, but by what you're expecting to hear. If you listen to it fresh, without seeing any of the alternatives beforehand, you will likely hear what it actually says. 

So what should you be hearing?

The audio is from a toy that is actually saying "brainstorm". The toy is a Ben 10 crab monster that regularly uses the phrase as it shoots mind powers out of its cartoon skull.