He equates "At the Zoo" and "Old Friends" to "Being for the Benefit of Mr. Kite!" and "When I'm Sixty-Four", respectively. Fornatale notes, however, that while "Sgt. Pepper" was notable for sonically colorful, psychedelic shapes, "Bookends" is starkly contrasted by moody, "black-and-white and gray" sounds. While concept albums were fairly common among rock groups at this time—such as The Rolling Stones' "Their Satanic Majesties Request", The Byrds' "Sweetheart of the Rodeo" and Iron Butterfly's "In-a-Gadda-Da-Vida"—"Bookends" enjoyed massive success with the format not unlike the Beatles nearly one year before. Garfunkel confirmed the influence of "Sgt. Pepper's" in a 2015 interview, commenting, "We were terribly impressed, and that shone a light on the path that led to "Bookends"." Simon often smoked hashish when writing, and he was convinced he must be high to write. He felt the drug had a negative effect and caused him to "retreat more into myself." He often found himself alone while on tour, and his thoughts grew dark during these times. He attributed "the pain that comes out in some of the songs is due to the exaggeration of being high." "Bookends" contains many of Paul Simon's major themes, including "youth, alienation, life, love, disillusionment, relationships, old age, and mortality". Simon's work on "Bookends" is loosely autobiographical, designed to function as both a personal and artistic statement. Simon, "feeling especially auteurist in the Dylan style of the day", had planned out the album's concept before he began writing, telling Garfunkel "I'm going to start writing a whole side of an album—a cycle of songs. I want the early ones to be about youth and the last song to be about old age, and I want the feel of each song to fit." "Bookends", originally released primarily as a vinyl LP, opens and closes side one of the disc with the "Bookends Theme", a brief acoustic piece (once compared to the work of English rock band the Moody Blues) that evokes "a time of innocence". "Save the Life of My Child" is a dramatic story involving drugs, violence and a mother-and-child relationship. According to James Bennighof, the song "deals with individual crises in crowded urban settings, along with references to larger societal forces and at least a hint of some transcendent perspective".