Oh, so is that how guitarists who use picks play octave double-stops, by just muting the note in between the upper and lower root? I play fingerstyle, see, and I play octaves by plucking the two notes simultaneously with my thumb and index finger; and I've always wondered how guitarists who played with picks managed to play octaves... I think I see now...

But I suppose that must seem patently obvious to the rest of you! :o