In the spring of 1965, dentist John Riley slipped LSD into after dinner tea for John Lennon, George Harrison, and their wives Cynthia and Patti. John Lennon later recalled the experience in a radio interview, which became the narration for this animation.
Rolling Stone has some thoughts from the others who were present, and the story of what happened afterward. John and George introduced LSD to Ringo that summer, but Paul resisted until the next year. That fact created some problems in the group as they worked on their next album, Revolver. -via Uproxx