It is basically a long build up where a man has a dairy farm that he wants to improve efficiency on. Guy goes to a bunch of different professionals to have them model it but none can make a working model, so on a whim he goes to a physicist. The physicist after toiling many weeks finally comes back and goes, "I did it and I'm not sure exactly what these constants mean or why, but the only way to make it work is if you assume the cow is a perfect sphere in a vacuum". It is a joke based on many equations that we use actually have very absurd assumptions.