If milk was meant to see the light, wouldn't cow's be see through?

The Cows in this commercial were crated in 3D using keyframe animation techniques. No motion capture or rotomation was employed. The animators spent time studying and observing Cows natural behaviors and movements and translated that knowledge into the performance of the Cows. There had to be special consideration given to the fact that the cows were hauling around a tonne of milk inside them. This provided challenges to the natural physics and motion of the Cows as while we needed them to at times move faster than a real cow could, we had to always be mindful of how realistic the simulation of the milk would be in that phase of the process. One way we managed to control this was to remove all lateral movement from the cows in the fluid simulation, imagine a Cow on a treadmill, enabling the motion of the milk to appear correctly in realtime without sloshing into a milkshake.