"The first thing you should know about working in a mortuary," the teacher said as he removed his latex glove and inserted a finger right up the ass of the body on the table, "You can't be squeamish." He then stuck his finger in his mouth.

The students grimaced as he motioned for them to line up and do the same. 

When the last student had stuck their finger- right up to the knuckle, the teacher insisted- and stuck the finger in their mouth, the teacher said- "The second thing you should know about working in a mortuary is attention to detail. I stuck my middle finger in, but sucked my index finger." 

The class was horrified. Some of them threw up. 

"The third thing you should know" the teacher said as he picked up his briefcase "is that I don't work here." 

"And the fourth thing you should know," said the man lying on the table with a smile, "Is that I'm not dead."