This is the best example for paying attention that I have ever heard.
First-year students at the Purdue University School of Veternary Medicine were attending their first anatomy class with a real dead pig. They all gathered around the table, the body was 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's body." For an example, the professor pulled back the sheet, stuck his finger in the anus of the sow, 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 seconds, but eventually took turns sticking a finger in the butt of the dead sow 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."