I feel certain, being myself a lover of Mr. John Barleycorn, that the refrain in question, "Musha ringum duram da, Whack fol de daddy-o," and so forth refers explicity to the thrashing and processing of the barley, wheat, and other grains necessary for the production of the "Whiskey in the Jar." Once must confess however -- after all this analysis -- it's a mighty fine song, sure 'nuff.