 It goes down six semitones from the IV (C chord) to a vii (Fm) [adding a non-G scale C#] then a V-of-vi (B7) chord [adding a non-G scale D] which briefly modulates towards a new tonic E minor.McCartney mostly sings a B note ("of her hand") over both Fm, where it is the eleventh, and the B7, where it is the tonic.When the sequence is repeated ("nobody can"), McCartney sings both B and C over the Fm, the C natural producing a tritone.