Oh, just Russia's greatest composer messing about with an expensive new toy.
A powerful, percussive chant has swiftly become the one of the most iconic moments of EURO 2016. And 10,000 people doing it in unison sounds incredible.
If you've seen any of Iceland's games in EURO 2016, you would've heard it coming from the stands. A Viking War Chant involving long pauses, clapping and the word "Huh" has become one of the most iconic symbols of the championships, chanted in celebration and encouragement by fans and players alike.
As ever, sheet music helps explain it all:
Iceland's footballers were the most unlikely quarter-finalists, eventually knocked out by the tournament's hosts, France. To welcome home their team, a crowd of over 10,000 gathered in Iceland's capital Reykjavik and let rip with the chorus, led by a sole drum.
And it sounded incredible: