It’s the quintessential Sixties acid song; the title’s words even spell out “L-S-D.” But John Lennon, who had always been candid about his use of mind-altering chemicals during the making of Sgt. Pepper, never relented from his claim that the song’s true and only inspiration was a picture his four-year-old son, Julian, painted of a classmate named Lucy O’Donnell. "I swear to God or swear to Mao or to anybody you like, I had no idea it spelled LSD," Lennon told Rolling Stone.