This is inspired by the [other question](https://academia.stackexchange.com/questions/16265/you-are-paid-to-answer-my-questions-how-to-handle-silly-questions) about dealing with stupid questions. The popular answers all seemed to assume that the student really wants to hear an answer. While this is a reasonable assumption, and the answers are very good, they don't cover trolls. 

Imagine that you are teaching a computer science lab and a student asks you why our noses run and our feet smell. I agree that you should act professionally no matter what the student does - but what behavior would be considered "professional" in such a situation?