I recently came across the term “development mule” in an article at Jalopnik, and several Ford Mustang “mules” were featured in director David Gelb’s A Faster Horse, which documents the design, production, and development of the 2015 Mustang. I was fascinated with the term, so I did a little research. According to Wikipedia, a development mule, test mule, or (simply) mule in the automotive industry is,
a testbed vehicle equipped with prototype components requiring evaluation. They are often camouflaged to deceive competitors and thwart a curious automotive press.
So what is the difference between a “prototype” and a “development mule?”