Students at a Medical School were receiving their first anatomy class with a real dead human body. They all gathered around the surgery table with the body covered with a white sheet.
Then the Professor started the class by telling them, In medicine, it is necessary to have two important qualities as a doctor. The first is that it is necessary that you dont get disgusted.

The Professor uncovered the sheet, sunk his finger in the butt of the dead body, withdrew it, and then stuck his finger in his mouth and sucked it.

Go ahead and do the same thing, he told his students.
The students freaked out, hesitated and subsequently taking turns, sunk their finger in the butt of the dead body and sucked it after withdrawing it.

When everyone finished, the Professor looked at them and told them, The second important quality is observation. I inserted the middle finger and sucked the index. Pay attention people.