Tommy Scott who was acting producer of Them sessions after Bert Berns returned to America described how "Mystic Eyes" came about in the studio as being originally conceived as an instrumental: "after blowing his harmonica for about seven minutes, Van suddenly burst into this spontaneous lyric." The ten-minute take was condensed to a single's length by cutting from the beginning and ending of the instrumental.
Tommy Scott, who took over as producer for Them sessions after Bert Berns left America, recounted how "Mystic Eyes" came about in the recording studio: initially conceived as an instrumental piece, it evolved when Van Morrison suddenly improvised a lyric after playing his harmonica for seven minutes. The resulting ten-minute take was later trimmed down to fit a single's format.