In Silver Blaze by Arthur Conan Doyle, Sherlock Holmes and Inspector Gregory have the following exchange:
Gregory: "Is there any point to which you would wish to draw my attention?"
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."
Sherlock Holmes aficionados know the answer to this mystery: the dog encountered its master and probably wagged its tail. Rereading this novel one more time