An autopsy professor was giving an introductory lecture to a class of students. Standing over a corpse, he addressed the class. "There are two things you need to make a career in medical forensics. First, you must have no fear." Having said that, he shoved his finger into the corpse's anus and then he boldly licked his finger. "Now you must do the same," he told the class. After a couple of minutes of uneasy silence, the class did as instructed, each student inserting a finger and then licking it. "Second," the professor continued, "you must have an acute sense of observation. For instance, how many of you happened to notice that I put my MIDDLE finger into this man's anus, but the finger I licked was my INDEX finger?"