One is the relative minor and major of each key. You know how a key like G major also has the same notes as E minor. The thing is they probably started the song with either G major or Ddom7, then when they got to the verse they maybe played either E minor or B minor.
The second one is the song may have been written in the Harmonic minor scale. Which the 5th chord in that scale is a dominant 7th chord (which is major sounding by the way, alittle mix of minor but dominantly major). Take the E harmonic minor chords.
Eminor / F#dim / G+ / Amajor/ Bdom7 / Cmajor / Ddim.
So if the song was in E harmonic minor (i dunno if it was but the rule applies regularless of the root), they may have started the sound with the Bdom7 (B7) chord and then started the verse with the root E minor chord.
Hope that helps. Latr
"My whole life is a dark room...ONE BIG DARK ROOM" - a.f.i.
