This sounds like what Bob Gibson and Bob (Hamilton) Camp used to do. They'd sing a verse with one of them singing melody, then they'd both sing harmony parts and let the "shadow" melody exist in the ear of the audience. I don't know if Ricky and Emmylou are doing the same thing, but I wouldn't be surprised. Interesting to hear about the ear naturally picking up the high part; that's always been my issue with trying to learn melody lines. It gets especially interesting when they switch the melody to the tenor on the last verse. You hear it loud and clear, but you're not sure what it is... Ray