When the film was originally released, an uncredited actor voiced Professor Moriarty, who remained in the shadows. After the release of A Game of Shadows, Moriarty's dialogue was re-dubbed by Jared Harris.
During the film Holmes and Watson are analyzing a pocket watch as a key piece of evidence. Their observations of the watch being scratched by a frequently drunken man's hand, and it being engraved by numerous local pawn shops is paraphrased from the classic Sherlock Holmes novel: The Sign of Four.
Watson points out that one of the vials of liquid in Holmes' possession is "used for eye surgery". In the late 18th century, cocaine was used as a form of medicinal treatment for multiple eye injuries and diseases. In the novels, Holmes is in fact, a cocaine addict.
To create the distinct sound of the film's soundtrack, Hans Zimmer used a broken piano.