Two thoughts:
1) I love Elvis slight shift in the original Bacharach lyric, "And the blue shadow will fall all over town." In the original, it's "the blue shadows," plural. Elvis's shadow is encompassing, specific, familiar—he's known it before. And it's a single shadow that sweeps over everything, in a vast hypallage. Of course, it is neither the city nor the shadow even that is blue. He is, and because he is, everything to him is colored that way. The shadow anticipates his blues, the depths of his depression.
2) Another piece of anticipatory rhetoric, "then my wild beautiful bird, you will have flown." The use of the future perfect signifies that by the time his love meets another man, she will already have been gone. Meeting someone knew here is the effect, not the cause of her departure. She is gone already, in fact. The singer is struggling to acknowledge what he already knows: love has already let him down, already he finds himself alone, and already his love has left. He is awaiting her material departure from his life as a sad formality.
Two thoughts: 1) I love Elvis slight shift in the original Bacharach lyric, "And the blue shadow will fall all over town." In the original, it's "the blue shadows," plural. Elvis's shadow is encompassing, specific, familiar—he's known it before. And it's a single shadow that sweeps over everything, in a vast hypallage. Of course, it is neither the city nor the shadow even that is blue. He is, and because he is, everything to him is colored that way. The shadow anticipates his blues, the depths of his depression.
2) Another piece of anticipatory rhetoric, "then my wild beautiful bird, you will have flown." The use of the future perfect signifies that by the time his love meets another man, she will already have been gone. Meeting someone knew here is the effect, not the cause of her departure. She is gone already, in fact. The singer is struggling to acknowledge what he already knows: love has already let him down, already he finds himself alone, and already his love has left. He is awaiting her material departure from his life as a sad formality.