Mostly composed by John, but Paul played the jangly lead guitar. I often confuse this 1965 song with Day Tripper. Both songs have a classic blues structure, both feature memorable lead guitar riffs, and both appear––on the surface at least––to be about transport. In reality, neither song has anything to do with travel, but in keeping with blues tradition both songs are heavily obscured references to sex.
Why hide references to sex under metaphors so obscure that not one listener in a hundred would be able to decipher them?
Perhaps because it's fun, perhaps because it's poetry, but more than anything, for a song to be a hit in the England of 1965 it had to played on the radio, and it seems unlikely that a song about a prostitute's health certificate would have got past the censors at the BBC.