This is from this month's Sound-on-Sound, tucked away in an article on the Clavioline (keyboard first made famous by The Tornados on their 1962 song "Telstar" by that account).
Apparently John was feeling "experimental" in the studio that day, and decided that rolling an orange up and down the keyboard was the perfect way to get the sound he wanted. That desperate, almost panicked to my ears, tone has always been one of my favorite Beatles sounds. It sounds almost like the instrument is about to burst!
Trivia for those who may not know but do care (probably not many of those on this forum!) ... this was one of the first songs they recorded outside of Abbey Road. Mick Jagger sang background vocals.
