The Academy Award that Sir Charles Chaplin won for composing this film's score is the only competitive Oscar he ever received; his other awards were given to him for special achievement outside of the established categories.
The flea circus act in the film was a comedy idea that Sir Charles Chaplin had conceived of in 1919. Originally, he used it in the one completed scene of an aborted film project called The Professor (1919). Later, he attempted to use the idea for Le Cirque (1928) and Le dictateur (1940), but could not justify it in either plot. Finally, in this film he was able to use the act.
The children in Calvero's first scene, the ones who tell him the landlady isn't home, are Sir Charles Chaplin's own children.
Sir Charles Chaplin worked for 2½ years on the screenplay and then devoted nine months to the score.
When some scenes were reshot, Claire Bloom was unavailable, so Sir Charles Chaplin's wife, Oona Chaplin, stood in for her. She can be seen lying in the bed through the doorway after the housemaid has told Chaplin's character that his "wife" isn't eating.