How to Interpret 'Cruel and Unusual'

Okay, so what constitutes "cruel and unusual"? Why was it okay to brand horse thieves in the face in old timey days, but it's barbaric now?

In the final installment of this year's Judge Week, we go over the history of cruel and unusual punishments; what scared the English into outlawing it in their Bill of Rights, and how America interpreted it for the first century of the Constitution. Then, landmark decisions which have further modified, narrowed, and evolved what constitutes as "cruel" in the United States.