A Border Patrol agent is on duty. He spots two Mexicans and runs them down. They show him their papers (he thinks they are phony). He tells them, "O.K. I have a test for you. I want you to use the words 'cheese' and 'liver' in a sentence."
So, the first guy says, "I made a liver and cheese sandwich for lunch."
The agent says, "That was good, you can go. What about you?" He asks the second guy.
He says, "Liver alone. Cheese mine."