The rule of the function seems to be applicable mainly to words representing animals, geographic locations, landmarks, and some other real-world concepts. The function seems to have limitations or inconsistencies when it comes to certain inputs like compound phrases (e.g. "Statue of Liberty"), technical names (e.g. "Mount Everest"), and non-concrete nouns like "soccer" or "basketball". Additionally, there are a few inputs like "cat" and "River" that should have an associated related concept, but the function does not provide a proper output or returns "Undefined"/"undefined".