It is the war cry that has taken Euro 2016 by storm. The roar of thousands, followed by a thunderous clap, then silence.
It has been likened to a Viking's battle cry, one which could easily sit in a Game of Thrones episode.
But apparently, this Icelandic chant is not very Icelandic.
Its origin remains ambiguous, with reports linking it to the Polish handball fans, while supporters of Scotland's football team Motherwell also do it.
And now, Icelanders have made it their own and with it, they are in one accord - or voice.
Icelander Thor Baering Olafsson, a travel agent, said: "Now everybody is doing it. Even the kids at kindergarten are doing it."
Another myth about the hair-raising chant is that it is not all about the roar and clap. Ironically, its power is in the silence.
Olaffson said: "You know, it's in the silence in between the claps - that's what makes the most tension and it creates that.
"There are no words and there's no meaning to it (the chant). It's like a Viking growl."
The rhythm and beats are set by lead drummer Johann Bianco, who will be heading a team of five drummers against France.
As to how he decides when to hit the drums, he goes by feel. The 35-year-old, who works with disabled children, said: "I'm a drummer in real life, been playing since I was a kid, often in rock or metal bands, so this just comes naturally. I just feel when the time is right to change gears and to go harder, better, faster, stronger."