According to the census: King Friday XIII's favorite color is purple and he can whistle. X the Owl's favorite color is blue and he can't whistle. Lady Elaine Fairchilde's favorite color is red and she can whistle.
As Mr. McFeely tries to make sense of the delivery mistake, he reveals that the customer number for the Neighborhood school is R144 and Mister Rogers' customer number is R143 - 1-4-3, referring to the I-Love-You code.
When Mister Rogers sets up the Make Believe models, he asks, "what have I forgotten?" In this instance, besides the trolley, he forgot the Platypus Mound.