The Beatles finished their American tour in late September 1964 and flew back to England. On October 8, on the way to Abbey Road Studios, McCartney came up with the Little Richard/Ray Charles–inspired “She’s a Woman,” and they recorded it for the B side of their next single. They stuck in a message for their new friend Bob Dylan, who had recently introduced them to pot, via a line about how McCartney’s woman turned him on when he got lonely. “Turn on” was slang for getting high, and Lennon recalled, “We were so excited to say ‘turn me on,’ you know, about marijuana and all that, using it as an expression.”

The record’s A side, “I Feel Fine,” was another of Lennon’s ebullient thank- yous to the fans, with a euphoric riff borrowed from Bobby Parker’s “Watch Your Step.”

Between the band’s resplendent harmonies and Starr’s drumming in the style of Ray Charles’ “What’d I Say,” the song was a guaranteed hit.

But for an extra twist, Lennon added a yowl of feedback to the intro, generating it by leaning his guitar against the amp. Critical consensus says that it was the first use of intentional feedback on a record. Maybe it was the marijuana that made him appreciate the beauty in sonic distortion, though he’d heard two other London bands use feedback before he started smoking pot.

Back on August 2, the Kinks had opened for the Beatles in Bournemouth, England. Kinks leader Ray Davies later recalled, “John Lennon made a remark that we were only there to warm up for them, but we got a great reaction to ‘You Really Got Me.’” The London band tore the house down with the song, which featured the most distorted guitar sound to date, thanks to guitarist Dave Davies’s slashed speaker cone. “It was an early validation that we had something that stood up for us, like being bullied in school and having something that was bigger than the bully, it was that sort of feeling.”

Two weeks later, on August 16, the Who, going by the name the High Numbers, joined the Beatles and the Kinks on the bill in Blackpool. Onstage, Pete Townshend shook his guitar in front of the amps to conjure a feedback maelstrom. But the High Numbers’ first single had flopped, and Townshend didn’t feel he had enough clout to ask the band’s producer to put anything avant-garde on their records. The Beatles’ producer George Martin, however, would prove extremely receptive to his group’s increasingly unusual ideas.

“I Feel Fine” shot to No. 1 on December 26, and stayed there for three weeks. Its brief five seconds of feedback reverberated like the jarring Emergency Broadcast System signal—then in use in the United States to verify that the airwaves were working properly—thus announcing that a new era of experimentation was about to begin.