I listened to Let It Be on 30 January and Let It Be... Naked on 31 January because according to Mark Lewisohn's The Complete Beatles Recording Sessions, some of the Let It Be songs were recorded on those two days fifty years ago. I noticed something about "For You Blue," but I had to do some research before I wrote about it.
About a minute in, George Harrison says, "Bop, cat, bop." I think this might be a bit of Gene Vincent's influence. Leading into an instrumental section in Vincent's "Bluejean Bop," he shouts to his band, "Bop, Blue Caps, bop." Harrison's "Bop, cat, bop" - spoken during an instrumental section - isn't too dissimilar. In the Anthology book, Harrison even mentions "Bluejean Bop" specifically (p. 49).
The Complete Beatles Recording Sessions and the Anthology 3 liner notes mention that the Beatles played through three Vincent songs ("Ain't She Sweet," "Who Slapped John?" and "Be-Bop-A-Lula") during the Abbey Road sessions (on 24 July 1969) but that "For You Blue" was recorded before this (on 25 January 1969). Anthology 3, however, also explains that "the version on the album Let It Be featured a lead vocal re-recorded by George on 8 January 1970." It's possible, then, that running through those Gene Vincent songs in July 1969 recalled "Bluejean Bop" and eventually resulted in the "Bop, cat, bop" in "For You Blue."
