This quote has always puzzled me a little bit because if Lennon thought take 7 was too heavy, why did they subsequently create an even heavier version? Wouldn't it make more sense to do a lighter version? Regardless, Martin agreed to write a score for four trumpets and three cellos, but before those could be recorded the band had to create a new backing track on to which the orchestral instruments could be overdubbed. On 8 December 1966, 15 additional takes were recorded (numbers 9 through 24 - takes 8 and 19 do not exist).
But those backing tracks weren't the only thing recorded that day. Producer George Martin and engineer Geoff Emerick had prior commitments that particular evening and thus could not attend the recording session until rather late. "When Geoff and I strolled in at about eleven, Studio No. 2 was in the grip of a controlled riot. The boys had decided it would be fun to lay down an 'unusual' rhythm track for 'Strawberry Fields Forever' on their own, with anyone and everyone available simply banging away on whatever came to hand. The racket as we walked in was like something from a very bad Tarzan movie. ... Above it all, Ringo was struggling manfully to keep the cacophony together with his regular drum-kit. The Beatles were at play, and here was I coming in to party-poop! ... Towards the end of this rogue track ... everyone was whooping or yelling, and John can clearly be heard chanting very slowly, and in time to the rough-and-ready beat: 'Cranberry sauce, cranberry sauce . . .' Why cranberry sauce? Why not? It was coming up to Christmas! Some of that wild and whacky recording survived through to the release of the record, and you can still hear John chanting these words, if you listen closely. This gave rise to one of those absurd Beatle myths: that Paul was dead. Instead of 'Cranberry sauce', people heard 'I buried Paul' " (Martin, page 19-20).
Indeed, at the very end of the released version of "Strawberry Fields Forever" you can hear John slowly drawling "cranberry sauce" (about 4 minutes in to this video):
Lewissohn, Mark. The Beatles Recording Sessions. Harmony Books, New York, NY, 1988.
Martin, George with William Pearson. With a Little Help From My Friends: The Making of Sgt. Pepper. Little, Brown and Company, New York, NY, 1994.