The opening track of a warmly (and maybe somewhat suspiciously) awaited sophomore album has to do several things: it has to suck the listener in immediately, before he or she has a chance to start analyzing what’s going on, and it then has to get the listener’s heart rate up high enough and the endorphins flowing strongly enough that he or she is carried irresistibly into the rest of the program. Not until about halfway through the album should the listener be able to stop and ask “So how good is this album, anyway?” ”Ready to Run” does that and more: it also offers a bit of complexity to throw off those gainsayers who might still consider the Dixie Chicks nothing but fluffy pop-country. The key to that complexity comes in the musical non sequitur that opens the song: several bars of droning, Irish-style fiddle, doubled by, of all things, a penny whistle. Then the acoustic guitar and snare drum come in, taking the groove well away from any Celtic influence and deep into greasy, countrified funk. When Natalie Maines’ irresistible voice chimes in, closely followed by tight harmonies and a tasteful Scruggs-style banjo, the effect is complete. Lyrically, the song is pretty much pop-country fluff. But you don’t realize that until halfway through, at least.