Metal fans are easily identified by their denim and leather and patches, their love of beer, and, of course, their headbanging.

Headbanging—which, for the uninitiated, consists of violently shaking one’s head in time to the music—is by no means unique to heavy metal, but is most closely associated with it. Photographer Jacob Ehrbahn provides an in-your-face look at headbangers letting go and rocking out.

Ehrbahn got the idea while on assignment for the Danish newspaper Politiken in 2012. He attended Copenhell, a three-day metal festival in Copenhagen and by the end of the first day knew the real action was with hardcore fans. The paper ran a six-page spread, but Ehrbahn thought there was more to the story. “It’s not often that you get an idea that you really think is something else,” he says. “I thought this was original and kind of surprising, and I liked doing it.”

The origins of the term “headbanging” and “headbanger” aren’t entirely clear, but some argue it dates to Led Zeppelin’s 1969 tour of the US, where fans often shook their heads along with the music. But as with all things metal, credit may well rest with Black Sabbath; singer Ozzy Osbourne and bassist Geezer Butler can be seen banging their heads during a concert in Paris in 1970. Lemmy, being Lemmy, has claimed term might have grown from the name of his band, Motörhead. And Angus Young of AC/DC is as famous for his headbanging as he is for his epic riffs and schoolboy uniform.

However it started, it is as much a part of metal as long hair, pointy guitars, and getting lost under the stage. Ehrbahn catches it in glorious detail, each portrait better than the last. In addition to Copenhell, he attended Metaltown in Sweden and Wacken Open Air in Germany a few times. Fans warmly received him, and most eagerly agreed to be photographed. “When I started out I was a little nervous, all these metal freaks, would they smack up my camera? People were so great,” he says.

The risk of injury is real. Several musicians—Slayer’s Tom Arraya, Megadeth’s Dave Mustaine, and that dude in Slipknot who does the sampling—have been injured by their headbanging, and studies have linked the practice to all manner of head and neck issues. So Ehrbahn was wise to be wary, because a Canon 1D Mark IV isn’t something you want to get whacked in the face with. For that reason, he generally avoided peering through the viewfinder and instead held the camera beneath his subject and moved in sync to avoid collisions.

Ehrbahn likened the crowds to “standing like fish in a barrel,” so he was constantly jockeying for position amongst the thrashing bodies. He was forever checking his flash settings to ensure he was getting enough light underneath all that hair, and focusing is a bitch when you’re caught in a mosh. It’s no wonder he ended up with some 14,000 frames, 67 of which ended up in the book Headbangers.

“Some other photographer might have another approach to a project like this,” Ehrbahn says, “They might ask the headbangers out and tell them to headbang, or put them in a tent, but to me it was just important to get it during the concerts and nothing pre-fixed or anything. I just walked up to people and put the camera in their face.”

As for Ehrbahn, he put the camera down and gave headbanging a try after a couple of drinks. He doesn’t recommend it unless you’re ready for the inevitable morning after neck-ache.