The rule seems to apply to inputs with a specific length, as we see a consistent output for inputs like "Rhine". However, for other inputs like "Tokyo", "apple", "Zircon", "The Grapes of Wrath", "The Barber of Seville", "phone", "Bear", "Wolf", and "Ankara", the function does not provide any output, suggesting that the rule does not hold for these inputs. 

It is important to note that the number of test cases provided is limited, so there might be more to the rule than what we can gather from this small sample of inputs. It would be helpful to gather more data and observe the pattern of outputs for inputs with different lengths to have a better understanding of the rule implemented by the function.