Why did the writers give Charles Foster Kane the title "Citizen"? This was a title everybody had during the French Revolution. It was meant to show that everybody was equal. During the Russian Revolution it was decreed that everybody was to be called Comrade--but to have titled the movie "Comrade Kane" would have made the pro-socialist theme too obvious.
You can find a lot of interesting ideas in Pauline Kael's Citizen Kane Book. See link below.
Brigid O'Shaughnessy in the Dashiell Hammett book is only about 21 years old, as you can tell from her initial interview with Spade in his office. Why did John Huston cast Mary Astor in the role when she was obviously about 35?
Was Sam Spade in any real danger of getting hanged for the murder of his partner Miles Archer? Was he is any real danger of getting hanged for the murder of Floyd Thursby?
Who was Joel Cairo representing? And why? Why would General Kemidov send him on a wild goose chase after the falcon if the General knew it was phony.
You could write an interesting speculation about how Brigid stole the falcon from General Kemidov. She refuses to tell Spade how she got hold of it.
Why did Brigid confess to Spade that she had shot Archer?