"What's the difference between the North American porcupine and the African porcupine," the society matron asked the zookeeper.
"The principal difference is the North American species has a longer prick."
This, as you might assume, distressed the matron who stormed immediately to the zoo manager's office. The zoo manager said, "Ma'am, I apologize for my staff's unfortunate choice of terms. What the keeper should have said is the North American species has a longer *quill*. In fact, their pricks are just about the same size."