"There were two struggles going on with this song: Paul and John fighting over whether it should even exist! [laughs] John called it 'more of Paul's granny music.' But there was my own struggle coming up with the sounds that should go on it.
"For the hammer bits, we actually had to rent a proper blacksmith's anvil. The thing weighed a ton, as did the hammer used to strike it. Ringo tried but he just couldn't hoist the hammer in a way that allowed him to hit the anvil with the correct timing, so Mal Evans [one of The Beatles' roadies], who was a large man, he wound up doing it.
"The other thing was the Moog synthesizer solos in the middle and end, which sound almost like a Theremin. The Moog was a fascinating new instrument for everybody - George, in particular, loved working with it - but Paul played these solos. He tinkered around until he got a really incredible, spacey sound that worked quite well."