A nice way to dig under obvious truths. I learned the basic technique here from Emily Schnee, from whom I learn so much. I have found that many students experience this as a revelation because it calls on them to question again and again when they are typically called on to give one answer.
Take a simple statement of an identity (I am a teacher), or a problem (I don't have enough time to do work I want to do), or just about any simple sentence (slugs leave a trail)...
The player says her/his sentence out loud, then one person asks "why?"