This episode borrows a plot point from Conan-Doyle's original short story "The Adventure of the Silver Blaze". Notably after the reveal, Holmes starts a sentence with "Curious..." The original story contains the following exchange.
Holmes: To the curious incident of the dog in the night-time. Gregory: The dog did nothing in the night-time. Holmes: That was the curious incident.
Holmes: To the curious incident of the dog in the night-time. Gregory: The dog did nothing in the night-time. Holmes: That was the curious incident.