Lennon, amused that a teacher was putting so much effort into understanding Beatles lyrics, decided to write the most confusing, unusual lyric he could. Lennon's childhood friend and former fellow member of the Quarrymen Peter Shotton was visiting, and he asked Shotton about a silly playground nursery rhyme that they used to sing when they were kids.
Shotton remembered the words:
"Yellow matter custard, green slop pie,
All mixed together with a dead dog's eye,
Slap it on a butty, ten foot thick,
Then wash it all down with a cup of cold sick".
Lennon borrowed a couple of words from the rhyme, added the three old unfinished ideas and the result was the lyrics to "I Am the Walrus". Beatles official biographer Hunter Davies was present while the song was being written and wrote an account in his 1968 book on the band. Upon finishing the lyrics, Lennon remarked to Shotton, "Let the fuckers work that one out.""
Ah, a man after my own heart!