Even though I am agnostic I still am in favor "an eye for an eye and a tooth for a tooth".

In this instance, a proportional tool should be used on the convicted defendant in the most appropriate similar location so that his pain can most closely approximate the pain of his victim.

A murderer should be put to death in the precise manner as his victim with the same lack of anesthetic.  Stabbing, ramming an arrow through the ear, (local crimes); whatever.

Someone convicted of assault should experience the same amount of pain, broken bones, etc.  in precisely the same manner with the same wait for medical attention as their victim.