“It was tricky to play,” Jimmy Page once said of “Black Dog,” foreshadowing the frustration of so many classic-rock bar bands.

The song opens Led Zeppelin’s untitled fourth LP with a hard-rock whiplash, constructed around a knotty, deceptively complex riff written by bassist John Paul Jones. It remains one of the band’s signature cuts, a true showcase for each member — but it took a Herculean effort to piece together that puzzle.

“I wanted to try an electric blues with a rolling bass part. But it couldn’t be too simple,” Jones later recalled to journalist and filmmaker Cameron Crowe. “I wanted it to turn back on itself. I showed it to the guys, and we fell into it.” But the shifting time signatures were tough to pin down — especially, as Page told SiriusXM in 2014, “the bit where it goes into sort of triplets in one part and overlaps.” Drummer John Bonham had the toughest job: figuring out how to lay down a solid groove amid such musical trickery. “We struggled with the turnaround,” Jones added, “until Bonham figured out that you just four-time as if there’s no turnaround. That was the secret.”

Robert Plant still had to carve out his own path into the maze. And one arrived through Page, who designed a call-and-response approach inspired by the a cappella/full-band dynamic of Fleetwood Mac’s 1969 single “Oh Well (Pt. 1).” The singer kept things simple, howling vintage-styled blues lines about making a lover “sweat,” “groove,” “burn” and “sting.” “Really if you’re asking me what my part of it was,” Page told SiriusXM, “it was actually taking it from a riff and making it into a piece of music — more constructed, more as a working piece so we could all sort of play it.”

And as the band’s producer, working alongside engineer Andy Johns, he was also crucial in shaping the track’s distinctive sound — from the opening helicopter-propeller tonal swirl to a crunching guitar tone that, according to 2018’s Led Zeppelin All the Songs: The Story Behind Every Track, nodded to Neil Young and Crazy Horse’s “Cinnamon Girl.”

To give his solo a left-field flavor, Page ran his instrument through a Leslie speaker — the end result has a silvery sparkle that jarringly jumps out from the backdrop, like a UFO swooping into a clear blue sky.

Much of the guitar work on “Black Dog” is noticeably sloppy — even for Page, a player who always prioritized feel and emotion over rhythmic and pitch perfection. Many of his bends on the solo are a tad sharp or flat, and he lands way ahead of the beat several times during the main riff (for example, around 2:43), giving that section a strange tension.

The Led Zeppelin IV sessions spanned December 1970 to February 1971, largely at the historic Headley Grange country house in Hampshire, England — and that laid-back, idyllic setting even seeped into the track listing: Notably, “Black Dog” was named after a roaming canine who kept drifting in and out of the studio.

Despite being such an oddly arranged piece, “Black Dog” was issued as a U.S. single, reaching No. 15 on the Billboard Hot 100. And by then it was already a set-list staple, having been debuted live (alongside “Rock and Roll,” “Going to California” and “Stairway to Heaven”) on March 5, 1971 — eight months before the album release. It stayed in the mix for the majority of the band’s run, and a deliciously nasty take highlighted their 2007 reunion at London’s O2 Arena.

Every one of those performances was riveting, but Led Zeppelin never quite mastered “Black Dog” — every version was a roller-coaster ride, and the twists and turns weren’t always smooth. But it's hard to imagine this enthralling tune without that sense of musical free fall.

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