Yes, we are running a complex fluid dynamic calculation. We are breaking the coffeeliquid apart into 50 million particles (I know, a gross simplification), all bound by cohesive forces, calculate Braunian molecular motion (depending on the coffee´s temperature), then apply adhesive forces (where the coffee touches the cup). Finally apply (varying with altitude and geographic location) earth gravitational force and aircraft motion´s force, and we get a fairly decent presentation of a moving liquid.
This will only cost you 50 to 80% of available framerate, dependent on your computer. We thought about making the effect optional, but we strive for utmost realism, and this one you just can´t go without (even though you may think you can)!
Enjoy the coffee! Jan