First-year students at the Purdue Vet School were attending 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 students freaked out, hesitated for several minutes, but eventually took turns sticking a finger in the butt 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 but it’s even tougher if you’re stupid."