- Executive Meddling: The famous opening paragraph (currently the main page quote) states that among Merricat's favorite things is the deathcup mushroom, with the only problem being that the deathcup mushroom does not exist. While on the surface it may appear to be Critical Research Failure, Jackson's original manuscript shows she used the correct name, the death cap mushroom. Her editor changed it because "deathcup" sounded better.
- Most Writers Are Writers: At the time Jackson was writing the novel, her husband (literary critic Stanley Edgar Hyman) had been working for thirteen years on his long-delayed critical work The Tangled Bank, on which his publishers had already given several extensions. In spite of this, he was constantly discovering new material he planned to work into the book, causing him to rewrite whole sections to accommodate it. This exasperated his publishers but tickled Jackson, who poked fun at her husband by incorporating his writing habits and rambling into the character of Uncle Julian and his exhaustive, never-finished book about the Blackwood murders.
- Castle and The Tangled Bank were eventually published in the same year. Jackson's book, which had only taken about two years to write, was an immediate bestseller and completely overshadowed Hyman's work.
- What Might Have Been: Jackson's original plan for the novel was to have Merricat and Constance as two unrelated adult women, one a spinster and the other unhappily married, who conspire to murder off the husband in order to live together in happy isolation. In the middle of plotting this version, Jackson became concerned that the main female characters might be Mistaken for Gay and changed them to two siblings...which, ironically, contributed to the perception that Constance and Merricat have an inappropriately close relationship.
- Merricat's name was originally Jenny. When the characters were revamped as sisters, Jackson changed the name to Merricat in a sidelong homage to her daughter Sally, whose pet name was Sallicat.
Trivia / We Have Always Lived in the Castle