you can see and hear the chords of the middle part… those are not G and D like everybody thinks… in the past with the original LP you could pan the stereo and hear that guitar more clear, here on youtube is almost impossible to hear it; you could think it as a D sus4 but the bass is in E, so it’s eadg that goes to D; I saw a guy in a Page Plant concert making this guitar keeping the E string on air also; There’s also another guitar making the notes GF# one octave below so when everybody hear the G high and this G lower it’s easy to believe that this is a G chord (or a E minor 7) but it´s not. if you play it like I say with 2 guitars and the bass, it will sound exactly as it is… so one guitar makes this fourth chord eadg that goes to D Maj and the other one makes G to F# notes.. in the first part I missed the F# note agaf#… agca… agaf# but you can see the next chords which already explain. am I clear??