A scene in this episode shows John throwing a pen to Sherlock, who catches it without even looking at it. Benedict Cumberbatch caught the pen on the first take (using a mirror so he could see it coming), but the cameraman was too slow and missed it. He got it again on the third.
Amanda, the secretary, is played by Olivia Poulet, who was in a 12 year relationship with Benedict Cumberbatch at the time of filming.
The following scenes were cut from the episode for time constraints, and are based on their appearance in the script:
- After the opening credits, and before the scene with John having a row with the checkout machine at the supermarket, a scene in which Van Coon jumps out of a taxicab upon getting home, darting into his building before the cabbie can ask him if he wants a receipt. He is seen rushing up the elevator, locks the chain bolt on the door, finds his SIG-Sauer P226 in a kitchen door, dashes into his bedroom, and jams a chair against the door.
- After Sherlock takes the jade hairpin from Van Coon's secretary, he and John return it to the museum, and the hairpin is added to the costume of the Empress Wu mannequin. He hands it to the museum director, while John hands Seb's check to Andy. A close-up shows Soo Lin Yao's name being added on to the list of museum benefactors.
The only episode of the series not to feature Mycroft or Lestrade. The latter is mentioned once by Sherlock the first time he speaks to Dimmock.
The concept of the coded cipher comes from the Sherlock Holmes novel "The Valley of Fear," but the plot, though it slightly resembles that novel's, also bears similarities to other Holmes stories, including "The Sign of Four." The cypher and the heel tattoos also match the key elements of "The Five Orange Pips."