I just wanted to report that some invisible geometry inside the mouth cavity is causing artifacts to be evident when using Traveller's lip corners back morph that he posted in his site. Using the group tool and magnets, I've only been partially successful in isolating the offending vertices, but their invisibility in some positions is making it very slow going. If someone has a way of making this mouth cavity geometry visible so that areas that break through the skin become obvious, it will make things easier to remedy these artifacts.