The sprawling, disjointed nature of 'I Am The Walrus' owes much to the fact that it is an amalgamation of at least three song ideas that John was working on, none of which seemed quite enough in its own right. The first, inspired by hearing a distant police siren while at home in Weybridge, started with the words 'Mis-ter c-ity police-man' and ran to the rhythm of the siren. The second was a pastoral melody about John in his Weybridge garden. The third was a nonsense song about sitting on a corn flake.

John told Hunter Davies, who was still researching the Beatles' official biography at the time: "I don't know how it will all end up. Perhaps they'll turn out to be different parts of the same song." According to Pete Shotton, the final catalyst was a letter received form a pupil of Quarry Bank School, which mentioned that an English master was getting his class to analyze Beatles' songs. The letter from the Quarry Bank pupil was sent to John by Stephen Bayley who received an answer dated September 1, 1967 (which was sold at auction by Christie's of London in 1992). This amused John, who decided to confuse such people with a song full of the most perplexing and incoherent clues. He asked Shotton to remind him of a silly playground rhyme which English schoolchildren at the time delighted in. John wrote it down: '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'.

John proceeded to invent some ludricous images ('semolina pilchards, elementary penguins') and nonsense words ('texpert, crabalocker'), before adding some opening lines he'd written during an acid trip. He then strung these together with the three unfinished songs he'd already shown Hunter Davies. "Let the fuckers work that one out", he apparently said to Shotton when he'd finished.

The 'elementary penguin' which chanted Hare Krishna was John having a dig at Allen Ginsberg who, at the time, was chanting the Hare Krishna mantra at public events. The walrus itself came from Lewis Carroll's poem 'The Walrus and The Carpenter'.

The 'eggman' was supposedly a reference to the Animals' vocalist Eric Burdon who had an unusual practice of breaking eggs over his female conquests while making love and became known amongst his musical colleagues as the 'egg man'. Marianne Faithfull believes that 'semolina pilchard' referred to Det. Sgt. Norman Pilcher, the Metropolitan police officer who made a name for himself by targeting pop stars for drug possession.