What noise is the crowd making at the Australian Open?
Instead of calling "booooo," which it certainly sounds like, crowds at the Australian Open are actually calling out "Siuuu" which has a completely different meaning.
So what does "Siuuu" actually mean?
"Siuuu" is far from negative—it's actually a supportive cheer which originated on the football field by none other than Cristiano Ronaldo, who is famous for calling out the sound after he scores a goal along with his signature jump and swivel in the air.
Ronaldo has previously said that yelling "siuuu" stems from the word "si", which means "yes" in Spanish.
How have tennis players reacted to the noise on the court?
Famed Scot Andy Murray was visibly angered when he heard crowds making the sound during his first match at the Australian Open, but when he learned what it really meant, his attitude changed drastically.
"First I thought they were booing me, but then I realised they were doing the sound Ronaldo does when he scores. It’s incredible," Murray told media.
Meanwhile Nick Kyrgios, who isn't unfamiliar with a little backlash was flummoxed for other reasons: "I can’t believe they did it so much," he said after winning his first round match.
"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."
Despite his comments, Kyrgios leaned into the atmosphere, even copying Ronaldo's trademark jump in the air after his win.
It's still unclear why the noise has made its way to the Australian Open, of all places. But that aside, we're all for a little extra support for the players as they give their all to the game. Here's hoping they've all done their research on what it actually means before they hit centre court...