There are many Science Fiction stories that contain elements of fantasy. For example, a wizard may appear in an episode of Star Trek. Conversely, elements of Sci-fi may appear in Fantasy stories. Additionally, it can sometimes be unclear whether certain story elements are essentially fantasy or scifi. For example, a fantastic phenomenon may go unexplained throughout the story, leaving it ambiguous whether the phenomenon could be explained from a sci-fi perspective (using real or fictional scientific principles) or from a fantasy perspective (using supernatural phenomena).