Finally, a fact that follows from both the up and the down sides of the soufflé principle: a fallen soufflé will rise again if put back into the oven. Those air bubbles are still in there, as is most of the moisture; and both air and moisture will expand again as the temperature goes up. You won’t get as high a rise the second or third time around, because the soufflé mix has stiffened and there’s less water available. But you can resurrect leftovers, or cook the soufflé once to set it and unmold it, then again to serve it.