You might have heard people shout "Siuuuu!" at some point over the last few years and wondered just what on Earth was wrong with them.
Or maybe you know that it stems from Cristiano Ronaldo's famous celebration, and still wondered what the hell was going on.
The Manchester United star is one of the most recognisable faces on the planet, and his celebration – where he jumps in the air, spins around, and lands with his arms outstretched by his sides – has become an iconic football image.
The noise he makes while he does it has also become something of an international phenomenon.
Cinema audiences at Spider-man: No Way Home have done it at crucial parts of the movie, Australian tennis fans have annoyed Andy Murray by doing it, and even Raheem Sterling's son has got in on the act.
What does Cristiano Ronaldo's "Siuuuu" celebration mean?
But where does the noise come from, and what does it mean? The Portuguese forward explains that it derives from "si", the Spanish for "yes".
"I started to say ‘si’, it’s like ‘yes’, when I was in Real Madrid," he once explained in an interview.
"I was in the USA and we played against Chelsea and I don’t know where this is coming from, the celebration.
"I just scored the goal and it just came out. It was just natural, to be honest. Since that, I started to do it more often and I feel like the supporters and the fans see it and they’re like ‘Cristiano, siiiiiiuuuu’.
"I’m like ‘wow! People are reminded of me because of it!’ So it’s good, and I’ll continue doing it like that."
The game against Chelsea is probably a pre-season friendly from 2013 – meaning that the famous "siuuuu" celebration is almost a decade old, and it's popularity seems to be going from strength to strength.
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Conor Pope is the former Online Editor of FourFourTwo, overseeing all digital content. He plays football regularly, and has a large, discerning and ever-growing collection of football shirts from around the world.
He supports Blackburn Rovers and holds a season ticket with south London non-league side Dulwich Hamlet. His main football passions include Tugay, the San Siro and only using a winter ball when it snows.