Some things are so familiar, so fixed in our heads, that we stop noticing them. Buckle-your-seat-belt instructions in an airplane, for example. You don't have to listen. You know the drill.
Here's another: "The Star-Spangled Banner." You vaguely hear the words, but all you're really doing is waiting to get to the "Play ball!" finish. Bombs burst in the air, rockets glare red, but nobody's feeling it. The words have gone empty.
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