If there's one trap that every GM falls into at some point, it's getting into a topic that one of the players is a genuine, certified expert on. Because you can guarantee that you will get something wrong, or use a technical term slightly incorrectly, or make some other mistake that nobody but a genuine, certified expert would even notice - and the player will pull you up on it, and go into great detail about just how amazingly, blindingly wrong you are.<br/><br/>Vergence (which is used in the movie) is indeed a real scientific term. In fact, it has a few different meanings in fields such as optics, ophthalmology, and, as we learn here, structural geology.<br/><br/>Unfortunately, as a GM, there's nothing you can do to avoid this problem, since RPG players tend to have diverse and obscure interests and professions. You may be lucky and have nobody in your medieval fantasy game be an expert on blacksmithing, but then someone will turn out to be studying pre-industrial tapestry making or something.<br/><br/>- Darths and Droids, strip 143. Curse you, Madpanda, and your backing in Chinese culture!