Stewie, Brian, and Lois "photobombed" the painting "A Sunday Afternoon on the Island of La Grande Jatte", by Georges Seurat. Grande Jatte is an island on the River Seine near Paris, and the painting represents the leisure time enjoyed by all members of society as a result of automation and improved working conditions brought about by the Industrial Revolution.
Stewie and Brian, as Holmes and Watson, discover the dead body of Kenny from South Park during the opening credits.
There was a satirical homage to a young Benny Hill, who in every one of his shows had a beautiful woman accidentally losing her dress before a chase scene would ensue.
Stewie begins to explain how he defeated Moriarty, but Moriarty was already dead. This is similar to a joke from Seth MacFarlane's movie 'A Million Ways To Die in the West.'
In his role as Sherlock Holmes, Stewie wears a deerstalker cap. The hat is never actually mentioned in any of Arthur Conan Doyle's stories, and largely became associated with Holmes because of pop culture depictions of him; as Watson describes, Holmes was quite fashion-conscious and, given his status in London society, would not have made the faux pas of wearing such a garment.