Unusual Book Ideas but most have been done

I met a retired person that was telling me she wrote a book immediately upon retiring. She knew the topic for her book. If I were to retire, I would like to write a book about some unusual topic. Here is a list of unusual book ideas. However, many books have been written about almost everything, including very unusual topics. Hence, my list includes many paranormal topics, hoping to find something new for whenever it is time for me to retire.

Book Topic	Book authors who already wrote it.
Someone real that got away with murder	Peter Lance
What really happened in the move Exorcist?	Troy Taylor
Spontaneous Human Combustion	Larry Arnold
Dreams	Craig Webb