So I was playing around today, sliding my pick up and down the string, then I started using a coloured pencil like a slide. And I found something interesting. If you hold the pencil/slide above the 12th fret, and apply just enough pressure to create a natural harmonic, you get the harmonic, but it sounds doubled. I don't know if there's any special name for this, but I thought it was kinda cool. Oh yeah, you probably want the gain cranked up to hear it best.