The Australian Open and Nick Kyrgios’s matches have been taken over by the ‘siuuu’ — so what is it?

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 Portuguese for some reason?

The answer is actually the latter, as the soundtrack to Nick Kyrgios’s raucous matches became the…