Observation

 
A professor is giving the first year medical students their first
lecture on autopsies, and decides to give them a few basics before
starting.

“You must be capable of two things to do an autopsy. The first thing  is
that you must have no sense of fear.”

At this point, the lecturer sticks his finger into the dead man’s anus
and then licks it. He asks all the students to do the same thing with
the corpses in front of them. After a couple of minutes’ stunned
silence, they slowly follow suit.

“The second thing is that you must have an acute sense of observation. I
stuck my middle finger into the corpse’s anus, but I licked my index
finger.”

Index