The first note was the first time feedback was used on a record. It was created when Paul McCartney pushed his bass up against an amplifier.
John Lennon wrote the majority of this song. It borrows from the " Watch Your Step" by the American Blues musician Bobby Parker. In 2008, Parker told the Forgotten Hits newsletter: "I've been in litigation for close to 55 years about some of this material that was stolen from me. They had 'Watch Your Step' on John Lennon's Jukebox and then that went out all over the country on PBS Television and people heard about it. John Lennon said how he had 'borrowed' that guitar part for HIS record, and pretty soon everybody knew about 'Watch Your Step.' I go over to England now and that's all they wanna hear, they don't even care about the new stuff I'm doin'. I'm out there playin' with Buddy Guy and Robert Gray, and they just wanna hear 'Watch Your Step' from John Lennon's Jukebox!"
The refrain is typical of Lennon's songwriting, with the three long notes: "I'm so glad." The sudden explosive refrain in harmonies is similar to Giovanni Gabrieli's grand concerto "In ecclesiis," an early baroque-music-piece. (thanks to Johan Cavalli, who is a music historian in Stockholm)
There is a very faint sound at the end of the song that was rumored to be barking dogs. It's actually just McCartney goofing around.
The Beatles taped this for an appearance on The Ed Sullivan Show that aired September 12, 1965. They had returned to America to play their famous Shea stadium concert. It was their last appearance on the show.