Teddy the street hustler is a nod to the Baker Street Irregulars, a gang of street urchins the original Holmes employed as lookouts and informants.
The note left for Sherlock by Moriarty reads (British spellings intact): "Men make plans, god laughs. I'm laughing at you now, as I always have. You think you honour me with your pursuit, you do not. You are a mouse chasing a lion, a mere planet in orbit of raging sun. - M"
First mention of the existence of Moriarty, Holmes's nemesis.
Guest star Vinnie Jones, a former professional football (soccer) player, played 42 times for Chelsea. Jonny Lee Miller is a Chelsea fan.
M is shown to be an Arsenal fan. Vinnie Jones, who plays M, is in fact a fan of Arsenal's most fierce rivals, Tottenham Hotspur.