Martian

Tell your class you are a Martian and you are inhabiting a human body to study human ways. You then ask about virtually anything in the room, and ask follow up questions: What is this? It's a pen. What's a "pen"? You use it to write. What is "write"? You make words with it on paper. What are "words"? ETC... You can make it as difficult as possible for your higher level students; at some point, though, you'll need to say "OK, I understand", and go to the next object. Even your best students will eventually get stuck on this one!