Hyde is, essentially, the most dark, evil, and bitter parts of humankind distilled into a single being of unimaginable malevolence and vitriol. Dr. Henry Jekyll has found a way to completely separate these parts of himself into a new and detestable being. It makes sense that this being would be—and he is—quite ugly, but it also makes sense that a person who confronts him in the flesh would be too overwhelmed with the sense that he is full of evil to take real notice of his exact features. It also seems probable that it would be difficult to look such an evil person in the face, and this would make it difficult for people to describe his features as well. In short, the fact that no one can accurately describe him has its roots in something akin to realism, but it also magnifies the sense of unpredictability and just plain weirdness about the man.