It takes something just said or just learned and reacts to it with astonishment, with the reaction following straight after: a million dollars on one video, that is insane; the Republicans raising the debt ceiling, unbelievable; they are still selling this, what a relief. It can also stand alone as an incredulous question, as in the line asking what on earth they mean about the stuff handed out on the plane. The news can be good or bad; what matters is that it is hard to take in.