First-year students at the Purdue      School of Veterinarian Medicine were attending their first anatomy class      with a real dead cow. They all gathered around the surgery table with the      body covered with a white sheet.
                              The professor started the class by      telling them, "In Veterinary medicine it is necessary to have two important      qualities as a doctor. The first is that you not be disgusted by anything      involving an animal's body." For an example, the professor pulled back the      sheet, stuck his finger into the butt of the cow, withdrew it, and stuck his      finger in his mouth. "Go ahead and do the same thing," he told his      students.
                              The students freaked out, hesitated      for several minutes, but eventually took turns sticking a finger in the butt of      the dead cow and, sucked on it.......followed by assorted gagging,      retching  and spitting, etc.
                              When everyone had finished wiping      their faces, the Professor looked at them and said, "The second most      important quality is observation. I stuck in my middle finger and sucked on      my index finger.  Now learn to pay attention. Life is tough but it's      even tougher if you're stupid."