Ah right. Yeah, I should know that since I parodied that song. Wasn't it in the movie, too?

Yes, it was in the movie - although not in its entirety. Mainly just the rhythmic guitar part was played during certain scenes. S & G also wrote a song about sitting on a Kellogg's Cornflake (Punky's Dilemma) and I always wondered if that came form I Am The Walrus, too. If not, then John and Paul (Simon) must have had very similar acid trips.