I see a hammer dulcimer in the background. But the main instrument, the Dan Bau, seems to be an analog theremin of sorts? Is this where Moog got the idea?

Theremins are analog already I know what you mean though, non-electronic.

It looks like an interesting instrument. Basically there is just one string, and it's plucked, and then the performer touches the string at various places along it's length to produce harmonics. The stick on the right side of the video is attached to the string, and you can increase or decrease tension, either to produce vibrato or to shift the pitch up or down (like a whammy bar on a guitar).

I wonder how hard it is to play.

I think it's probably pretty hard to be as accurate as she is. You can try it out with a rubber band anchored at one end and the other in your hand and stretch it to increase and decrease tension while strumming it in the same way and see how many notes you get dead on when you try to play a song. Of course, shaking it to get vibrato kind of helps put you in the range of the note so you can make small adjustments without being too obvious. But still, she's impressively accurate, and this clearly sounds way better than your rubber band will.

She's not controlling the pitch merely by stretching the string. Actually she's getting most of the pitch by hitting harmonics. You can produce these on a guitar, or most other stringed instruments. They are merely points along the string where you can touch a moving string, and change the pitch by adding sort of a standing harmonic wave. The easiest one to hit is one octave and obviously that's right in the middle of the string. On a guitar there are other good places like the 5th and 7th fret.

Still, on a single string, to be able to hit that many notes is quite an accomplishment.

I see. Interesting stuff. Thanks for the info.