Case Keenum opened up his arms by his side. Then he brought them together above his head, and held them there, just for a split-second. A split-second to ensure some 66,000 Minnesota Vikings fans recognized what he was about to do. A split-second to ensure they’d join him in one of the most stirring moments of the NFL season.

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Then Keenum dropped his hands. Then he brought them together again. Down, up, down, up, rigidly yet rhythmically, his pace gradually quickening. And suddenly, all around him, his purple-clad followers were falling in line.

“SKOL!” Silence. “SKOL!”

There are several solid NFL chants. Some great ones, even. Keenum and his spontaneity lifted the Vikings’ “Skol” clap into the upper echelon.

But their opponent in Sunday’s NFC championship game, the Philadelphia Eagles, have a darn good rallying cry of their own. It can be just as spontaneous. It might not have the awe-inspiring potential of the Skol clap, but it’s far more organic.

You hear it after ever Eagles touchdown at Lincoln Financial Field. You’ll likely hear it Sunday.

“E-A-G-L-E-S Eagles!”

But make the trek to Philly, and you’ll hear it elsewhere, too. You’ll hear it at bars; at Sixers games; in line at cheesesteak establishments, from Jim’s to Geno’s to Dalessandro’s; on the Broad Street subway line; heck, this time of year, you might even hear it out on Broad Street itself.

All it takes is one person. That’s the beauty of it. One person, one letter. “E!” It has almost become a universally understood cue in the City of Brotherly Love. “A!” Anybody within shouting distance joins in. “G!” It gathers momentum, crescendoing, hitting full flight around the “L!” And it never tails off. “E! S! Eagles!”

It’s not exactly creative. It has no special meaning. To many outsiders, it probably sounds like a random drunken refrain that caught on precisely because it was a random drunken refrain. But in a way, that’s exactly what makes it great.

It wasn’t part of a team campaign to better gameday atmosphere. There’s no single accepted origin story. One day at the notorious Veterans Stadium in the 1980s, it just … started.

“It was in the early ’80s at the Vet,” Jim Gallagher, a longtime Eagles employee, told Philadelphia Magazine. “One section would do it, and then others would start. It wasn’t a very organized thing.”

It has become an organized thing over the years. In the late 90s, a parking lot band coined the lyrics to “Fly Eagles Fly.” The band eventually became the official Eagles Pep Band, and the song became the team’s official fight song. And every time, without fail, it is topped off by an “E-A-G-L-E-S Eagles!”

The Vikings’ Skol clap has developed along a contrasting trajectory. It’s gone in the opposite direction. When it came to U.S. Bank Stadium at the beginning of the 2016 season, it was neither original nor spontaneous.

It was co-opted from Iceland’s national soccer team. The “Viking clap,” or “Thunderclap,” or “Viking war chant,” went mainstream during Iceland’s Cinderella run at Euro 2016. Players and fans coordinated it with one another after games. Its most rousing rendition came at the team’s homecoming party in Reykjavik:

The Minnesota Vikings then introduced their fans to it at the home opener months later. They did so with a big-screen video that featured clips of Iceland players and fans. Aron Gunnarsson, the captain of Iceland’s soccer team, explained the tradition to the sold-out crowd. Icelandic strongman and “Game of Thrones” actor Thor Bjornsson also helped out. Both were wearing Minnesota Vikings gear in the video. The team even got Bjornsson to crush a Packers helmet in theatrical fashion.

Hall of Fame quarterback Fran Tarkenton then instructed the crowd to clap along with the beat of the drum, and to yell “Skol,” a Danish, Norwegian, and Swedish salute that roughly equates to “cheers.”

It’s unclear if Iceland was the first to use the chant in a sporting context. Either way, the Vikings certainly aren’t the first to adopt some form of it. They’re not even the first American sports team. Seattle Sounders fans have a similar coordinated routine:

Nonetheless, Vikings vice president of content and production Bryan Harper said hundreds of fans emailed the team after seeing the Iceland chant, and it was too good to pass up. They now perform it in unison before every home game.

But lately, Keenum seems to have pioneered the spontaneous aspect. He led a brief Skol clap with traveling Vikings fans as he walked off Lambeau Field in Week 16:

Last Sunday took it to another level. There was nothing premeditated about the Keenum-led clap. It was impulsive. It was driven by passion. It gave millions of viewers goosebumps.

If not for that moment, “E-A-G-L-E-S Eagles” would have the upper hand in a contest between the two rallying cries. And its roots and backstory still do have the upper hand.

But, all else equal, including context and situation, there’s nothing like the raw tribalism of the Skol clap. There’s nothing like the serenity in between claps, and nothing like the explosions that interrupt them. Vikings fans haven’t perfected it, but they’re well on their way to making it the best chant in the NFL.