Sherlock Holmes: If you eliminate the impossible, whatever remains, however improbable, is the truth.
When Holmes and Watson are arguing in the kitchen, Watson puts her mug and phone on the counter. A few times during the scene, the mug switches which side of the phone it's on. The first time it's plausible Watson moves it when off camera, but subsequent to that, we can see enough of Watson to tell she doesn't make enough movements to change the position of the mug.
Sherlock's brother Mycroft has an international franchise of restaurants called Diogenes. This is a reference to the Diogenes Club, the gentleman's club Mycroft co-founded in the Holmes short stories.