At a drug-fueled party on Aug. 24, 1965, during a break in the Beatles' North America tour, John Lennon and George Harrison each took his second LSD trip. Ringo Starr tried the psychedelic drug for the first time, but Paul McCartney, wary of its effects, chose to abstain.

Before the day ended, Harrison would learn more about Indian music. He had started to develop an interest in it during the filming of Help! He would soon incorporate into his music and popularize in the West. Lennon would be inspired to write "She Said She Said," the iconic song from Revolver.

The crush of fans and police around the Beatles’ rented Beverly Hills mansion made it difficult for the band to leave. Instead, celebrities like Roger McGuinn and David Crosby of the Byrds and actor Peter Fonda came over and spent the day tripping with the three Beatles. (In 1965, LSD was still legal in California.)

Harrison and Starr discussed the band's drug use in The Beatles Anthology. Though they had been smoking marijuana for a year after being introduced to it by Bob Dylan, LSD was unknown to half of them. A few months earlier, Harrison and Lennon had taken their first acid trip at a dinner party thrown by Harrison's dentist, who had slipped it into their drinks. The two were profoundly changed by the experience.

"John and I had decided that Paul and Ringo had to have acid, because we couldn't relate to them any more," said Harrison. "Not just on the one level — we couldn't relate to them on any level, because acid had changed us so much. It was such a mammoth experience that it was unexplainable: it was something that had to be experienced, because you could spend the rest of your life trying to explain what it made you feel and think. It was all too important to John and me. So the plan was that when we got to Hollywood, on our day off we were going to get them to take acid. We got some in New York; it was on sugar cubes wrapped in tinfoil and we'd been carrying these around all through the tour until we got to L.A."

"I'd take anything," added Starr. "It was a fabulous day. The night wasn't so great, because it felt like it was never going to wear off. Twelve hours later and it was: 'Give us a break now, Lord.'"

"Paul felt very out of it, because we are all a bit slightly cruel, sort of 'we're taking it, and you're not,' Lennon told Rolling Stone. "But we kept seeing him, you know. We couldn't eat our food, I just couldn't manage it, just picking it up with our hands. There were all these people serving us in the house and we were knocking food on the floor and all of that. It was a long time before Paul took it."

McGuinn told the Daily Telegraph that a conversation he had with Harrison would influence the development of psychedelic rock. "We went in and David, John Lennon, George Harrison and I took LSD to help get to know each other better," he said. "There was a large bathroom in the house and we were all sitting on the edge of a shower passing around a guitar, taking turns to play our favorite songs. John and I agreed 'Be-Bop-A-Lula' was our favorite '50s rock record.

"I showed George Harrison some Ravi Shankar sounds, which I'd heard because we shared the same record company, on the guitar. ... You can hear what I played him from the Byrds' song 'Why.' I had learned to play it on the guitar from listening to records of Ravi Shankar."

Harrison has said, however, that it was Crosby who first mentioned Shankar's music. With the amount of drugs consumed, it's easy to understand the confusion.

Listen to an Early Version of the Beatles' 'She Said She Said'

Though the Kinks and the Yardbirds also experimented with the sitar at the time, the Beatles' "Norwegian Wood (This Bird Has Flown)," which was recorded in October 1965, was the first Western rock song released to feature the sitar.

"I went and bought a sitar from a little shop at the top of Oxford Street called Indiacraft – it stocked little carvings and incense," said Harrison. "It was a real crummy-quality one, actually, but I bought it and mucked about with it a bit. We were at the point where we'd recorded the 'Norwegian Wood' backing track and it needed something. We would usually start looking through the cupboard to see if we could come up with something, a new sound, and I picked the sitar up – it was just lying around. I hadn't really figured out what to do with it. It was quite spontaneous: I found the notes that played the lick."

In 1965, four years before his starring role in the film Easy Rider, Peter Fonda was hardly a household name. It was his friendship with the Byrds that allowed Fonda to attend the party, and he unintentionally influenced a future Beatles song.

"This was the second time they had taken LSD, and George was having a tough time," Fonda tells Empire magazine. "David Crosby comes up to me, and I don’t know why Crosby thought I wasn’t loaded, but he said, 'You have to go down and help George.' Why am I the tour guide? I went down and I said, 'George, don’t worry about it. This is a drug that makes you feel like dying and your brain doesn’t want to do that, so it's trying to stop and that’s the conflict so just let it go and ease out.'

"Then I said, 'I know what it's like to be dead, because a month before I turned 11, I shot myself in the stomach by accident and I died three times on the operating table while my heart stopped, so I'm still here to tell you the story.' I was trying to tell George, 'Don’t worry about it, just let, let the drug take you down the trip.' And John was sitting right there, looking at me as I told George several times, 'It’s okay, George, I know what it’s like to be dead.'

"We didn't want to hear about that!" Lennon told Playboy. "We were on an acid trip and the sun was shining and the girls were dancing and the whole thing was beautiful and '60s, and this guy — who I really didn't know; he hadn't made Easy Rider or anything — kept coming over, wearing shades, saying, 'I know what it's like to be dead,' and we kept leaving him because he was so boring! And I used it for the song, but I changed it to 'she' instead of 'he'. It was scary. You know, a guy … when you're flying high and [whispers] 'I know what it's like to be dead, man.' I remembered the incident. Don't tell me about it! I don't want to know what it's like to be dead!"