You have two men in a room. You know for a fact that one is a physicist and the other is a plumber. Sadly both men have recently been rendered totally deaf and haven't learned sign language. This is a problem because you have to tell which one is the physicist who can bring the run-away LHC under control and which is the plumber here to unclog the toilet.
You have a piece of paper and a pen. What single word do you write down and ask them to say to determine which is which?
Anyone that says plumber or physicist shall be squashed under an irrelevant elephant.