The interpretation we use is that a mule skinner did not skin the mule, but was skilled enough with the whip to flick a fly off the mule just barely touching the mule's skin. Enjoyed reading about the interpretation of the word "skin" meaning "to outsmart". I am one of the mule drivers (we say drivers)and historical interpreters on the canal boat ride at Easton, PA. I will be sure to mention the "outsmart" definition in my talk.