A friend sent me via email:

The Dead Cow And Vet School

First-year students at Texas A&M's Vet school were receiving 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
the animal body." For an example, the Professor pulled back the sheet, stuck his finger
in the buttocks of the dead 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 buttocks opening of the dead cow and sucking on it.

When everyone finished, 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's tough; it's even worse if you're stupid."