I'm sure a lot of you have heard Weeping Harp Senoh's "Spokey Dokey" which has inspired a lot of people to pick up the harmonica. I found an alternate take version on youtube.
This is a technique I have heard used on train songs a few times to simulate the "steam" being released.
I have replicated something similar before by opening my lips right off the harmonica, keeping my teeth together and hissing through your teeth and the harp "sssssssssss". Then bringing it to an abrupt end by closing my lips back onto the harmonica and stopping the air flow "sssssssssssspp". In your example it sounds like he is rolling his tongue too.
I guess the important bit is taking your lips off the harp in order to let the air out around the harp, allowing the hissing.
Here's a couple of other examples of similar technique being used.
At the moment, my only D is in pieces, so I could be wrong. But I am 99% sure he's playing a combination of 1, 2 and/or 3 draw followed by 3 draw. Also, he seems to be deliberately thinning the tone, either by lifting the jaw, and/or by pushing the tongue forward.
When you're trying to figure this stuff out, the task is a trillion times easier if you first establish the tonic note, or the key the piece is in. As you no doubt know, in blues, most of the time, that will mean going through your harps and playing 2 draw until that note matches the notes on the recording where the phrases/verses end.
If you do that with this piece, then it's quite easy to hear what's going on, i.e. the chord on the tonic (or I) followed by the interval of a major 3rd (or doh and me of doh rey me, etc). ---------- YouTube ditties
