I’ve notinced that it works better with wet lips but can’t imagine why that would matter.
WAG: The moisture acts like a lubricant and allows the air to travel faster over the lips by reducing friction.
WAG: It might also have something to do with the closed parts of the lips becoming airtight.
Huh. I just tried whistling first with normal, slightly damp lips, then dried off the open parts, then dried the whole lips, and then panted heavily for a minute or so to dry the whole mouth and tried again. It did not seem particularly harder to me, and nor did it sound any different. Flaw in the original premise?
Like Chronos, I find it doesn’t seem to make a great deal of difference. In cases where it does, might it have to do with moisture making the lips slightly more flexible?
I don’t know if it is suggestion, or tubulence, but it seems a tiny bit easier to get an original tone with wet lips, and control of pitch is similarly slightly easier.
Not in a range that satisfies me as proof either way, though.
Tris