The theory behind snifters is that they will allow you to smell your whiskey better. You take your hand, cup the glass, and by virtue of your body heat, heat up the whiskey (no ice, please). This increases the rate of evaporation of the alcohol, which is the primary transit method of the aroma via whiskey congeners, which are responsible for the oak and other smells.
I was responsible for the gaseous stage analysis - what happens to the fluid flow once evaporation has happened. I started with the cylindrical Navier-Stokes equations and continuity, made a bunch of assumptions and boundary conditions, and started simplifying. What finally popped out at the end was a familiar equation for pipe flow, and I threw in a little twist to account for the angle of the snifter walls.
So, as you can see, the flow really is governed by the pressure gradient, and the glass geometry acts as a converging nozzle, just as expected. A fun little analysis, one that intuitively makes sense, but now at least I have the math to back it up. Here is a link to the presentation.