[gravitas]

I've got a question that doesn't exactly follow the strain of conversation, but is related nonetheless.

There are other Harmonics than those that occur at the 5th, 7th, and 12th frets. The 2nd, 3rd, 4th, 9th, 15th, and 20th all have their own sounds. They're just more difficult to hear.

I'm interested in learning to make these sounds, as they're the spacey, robotic sounds you hear in songs like Frank Zappa's Black Napkins, or sprinkled throughout either of the Mars Volta's studio releases. Apparently, if you pump your treble up far enough and give yourself a little feedback, they're easier to hear, but as far as offering anything musical- see Black Napkins as an illustration as the sounds I'm trying to produce- I haven't the foggiest.

Any ideas?