You say hi, I say low....
The following is from the the Hello Goodbye song wiki.
The song originated when, in response to a question from Beatles aide Alistair Taylor about songwriting, McCartney sat down at a harmonium and asked Taylor to say the opposite of whatever he said. The completed song includes a musical coda, which was improvised by the Beatles when they were recording the track in October 1967. Unimpressed with the composition, Lennon pushed for "I Am the Walrus" to be the single's A-side, before reluctantly accepting that "Hello, Goodbye" was the more commercial-sounding of the two sides.