In the final scene of the movie Billie and Paul are pulled over by a motorcycle cop. There are three shots, one of them driving to the curb, one of them talking to the officer, and then driving away. The officer who talks to them is obviously much older (and bigger) than the thin young man in the first and third shots.
After Mr. and Mrs. Hedges leave, Billie goes out of the room dancing to the sound of the radio, with a lit cigarette in her left hand. The next shot shows her entering in the other room with no cigarette at all.
While visiting the Library of Congress in Washington, DC, Paul Verral explains to Billie Dawn that the country's whole government is based on "these three pieces of paper." In reality, the Declaration of Independence, the Constitution, and the Bill of Rights were written on vellum, or parchment, which is made of stretched and treated animal skin.
When Harry and Billie turn the radio on and off repeatedly during the Congressman's first visit, they alternate between using the left and right knob on the radio (actually they don't touch either knob but just wave their hands in the general vicinity of them).