Gifs are short, silent animations. Unlike videos, they carry no sound files within them. Which is why it's extremely odd that a lot of people online claim to be able to hear one.

It's a gif you've probably seen before as it resurfaces every few months, always with a similar caption: Someone asking "why can I hear this", usually accompanied by a few crying faces to show how distressing they find the experience.

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The gif, created by Twitter user Happy Toast, has resurfaced again after a scientist put out an appeal for help understanding why people hear a noise.

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Can you hear it? You're not alone.

Dr Lisa Debruine, a researcher at the University of Glasgow, also included a poll to see how many people could hear the gif. So far, 75 percent have said that they could hear a thudding noise.

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A further 4 percent have said they hear "something else" when watching the gif.

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So what is going on?

Well, first off, it's definitely not just this gif. Other gifs have been posted all over the Internet that people have claimed they can hear, such as this one where you can hear elephants on a see-saw...

... and this gif you can't look at without hearing the Queen classic We Will Rock You.

Gif credit: Twitter - Carolyn Dramos Instagram - Somaramos.