Have you caught yourself wondering what all that interminable noise at the Australian Open this year has been?
Are the crowd saying boo? Boo-urns? Or are they speaking Spanish for some reason?
The answer is actually the latter, as the soundtrack to Nick Kyrgios's raucous matches became the uniform cry of "siuuu".
Confused? You're quite right to be. Here's a bit of background.
What is this 'siuuu' then?
It all starts from Cristiano Ronaldo, one of the greatest footballers of all time.
During his time at Real Madrid early last decade, he began celebrating goals with cries of "si" — "yes" in Spanish — which eventually morphed into a more guttural "siu".
He continued that celebration through his time with Juventus and now with Manchester United, and in that time it became somewhat of a trademark.
Opposition players and fans have adopted it on occasion too, mostly to try to get under Ronaldo's skin.
So why was the crowd doing it at Kyrgios matches?
That's a really good question. There's no obvious reason for why it started at the tennis, and even Kyrgios himself said he was surprised to see it catch on.
Kyrgios did egg the crowd on after his win over Broady, replicating Ronaldo's celebration on court.
That was probably enough to ensure the "siuuu" was back in force for the Medvedev match.
What do the players think of it?
They all seem to hate it, and many of them seemed to think they were being booed initially.
After his second-round win over Kyrgios, Medvedev took a light-hearted pop at the crowd and left a parting message on the camera.
"[Jeering] between first and second serve, that's where, you know, it's tough," Medvedev said.
"It's not good for the game I think to do it, because probably people don't know, but when you're getting ready for the second serve, it's a tough moment.
"I think people should respect both players and just, you know, don't talk in these moments.
British veteran Andy Murray isn't a fan either.
"After a few times it was like, no [they're not booing] they're doing that, I think it's like 'siuuu' or something, that Ronaldo does when he scores," he said.
"It was incredibly irritating."
But for Kyrgios, who likes his crowds as vocal as possible, it wasn't all bad.
“They actually weren’t saying ”boo”. It’s just a stupid [chant],” he said.
“I can’t believe they did it so much. They were doing some Ronaldo thing. Ronaldo does it every time he scores.
“It’s like, I thought they were going to do it for like 10 minutes — they did it for two and a half hours. Like every point, I don’t know why. It was a zoo out there.”
