Sherlock Season 4: 18 Easter Eggs & References From 'The Lying Detective'

At Smith's hospital, John encounters Nurse Cornish. In a funny scene, she doesn't believe that he writes the famous blog about Sherlock's cases. Once she finally does accept who he is, she then criticises his work: "It's gone downhill a bit, hasn't it?"

This might seem like a dig at the Sherlock fans who complain online that the show is past its best, but it actually refers to an incident that happened to Conan Doyle.

I'll let Mark Gatiss explain:

"There’s a little joke in there about Nurse Cornish, who’s named after the Cornish boatman... Famously, when Conan Doyle’s being rowed across a river in Cornwall, this man says ‘do you write Sherlock Holmes?’ “And he said yeah. And [the man] goes ‘he was never the same after he came back from the dead, was he?’ So he was the first kind of critic.”