Following the death of Brian Epstein on 27 August 1967, The Beatles regrouped at Paul McCartney's London home on 1 September 1967, where the decision was made to continue work on the Magical Mystery Tour project.
Four days later they began work on one of the soundtrack's highlights, John Lennon's surrealist masterpiece I Am The Walrus. Sixteen takes of the rhythm track were recorded during this session, which began at 7pm and ended at 1am the following morning.
Lennon played electric piano, McCartney played bass on the initial takes and later switched to tambourine, while George Harrison was on electric guitar and Ringo Starr played drums. Lennon also sang a guide vocal to help the band follow the song.
At this stage there was an extra bar prior to the "Yellow matter custard" verse, which caused the group some problems when performing. They were supposed to play a C major seventh chord during the bar as a transition back to the verse, as heard on Anthology 2, but had trouble remembering the change. The bar was eventually removed during the editing stage.
Eventually The Beatles recorded a satisfactory version - take 16 - which was given further overdubs on the following day.