pinched harmonics on a cigar box guitar

You'll probably already know that if you pluck a string on a standard guitar and quickly touch it at the 12 fret, you get the harmonic and octave higher. You can also find harmonics on the 5th and 7th frets easily too. Well heavy metal players make use of this phenomena to get those high pitched squeals common to that genre using method know as "pinched harmonics". It's a bit of a dark art to me so excuse my ignorance on just exactly how they produce it. There is a definite techinique which I'm noy 100% sure on.

Anyway, I was just messing about with my CBG and found a way of getting an unusual harmonic which I think is similar to pinched harmonics. It sounds unusual because you can get it to sing out whilst sliding. It involved using thumb and forefinger at the same time to pluck the string. Sort of plucking it in two places with these digits but in opposite directions. I posted a short vid on my Youtube site using it. Have look and take note of what my right hand thumb and forefinger are doing when I'm getting the harmonics.

http://www.youtube.com/watch?v=JTIcHCVSzyA