"If I Fell"

I listened to the second disc of On Air - Live at the BBC, Vol. 2 to-day and noticed a small feature in "If I Fell" that's also present in the studio version.  Throughout the song, Lennon and McCartney are singing alternatively in unison and in harmony.  At the end of the line "When she learns we are two," they break from unison singing to harmony (on "two," Lennon sings a C; McCartney an E).  This musical break mirrors the fracture in the lyric itself.  That Lennon's C is an accidental (the song is in D major) highlights this break.