This is the best example for paying attention that I have ever heard.

First-year students at the Purdue University 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 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 an animal's body."

For an example, the professor pulled back the sheet, stuck a finger in the butt of the dead cow, withdrew it, then 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 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 my middle finger in the cow's butt and sucked on my index finger.  Now learn to pay attention.  Life's tough but it's even tougher if you're stupid."