"Postmortem dissection can only teach you so much about how the body works, and especially what it does when faced with stress." The word 'stress' is doing a lot of heavy lifting here. "While surgery is done under anesthetic, it's important to recognize less obvious signs of pain. Tightening of muscles that can't be attributed to anything else, the skin changing color, the quivering of the bowels. It's all useful information."