In-joke: In "General Hospital", General Melchett ('Stephen Fry') tells Blackadder (Rowan Atkinson) that "Oxford is a right dump". Like Melchett, Fry went to Cambridge University while Atkinson went to Oxford.
Tim McInnerny's character was originally named Captain Cartwright. Stephen Fry had the idea to change it to Darling (named after a boy at his school) and created a running gag which is frequently used throughout the series.
Tim McInnerny affected a nervous tick in his eye for the character of Captain Darling, but after the six-week rehearsal and shooting schedule was over, the tick had become second nature and it took him a further two months to get rid of it.