Revealing mistake: To demonstrate that "Clean This House" isn't a real company, Sherlock shows the man his phone displaying a 404 "file not found" message. Except the browser bar at the top simply shows "Clean This House", not a website domain. As written, he's just searched for the phrase, not tried to load a website.
Elementary (2012)
1 revealing mistake in season 3 - chronological order
Starring: Lucy Liu, Aidan Quinn, Jonny Lee Miller, Jon Michael Hill
While You Were Sleeping - S1-E2
Other mistake: When Sherlock was slapped, he later says he was surprised because the girl who slapped him was a "lefty." Then he rubs his right cheek and says it's leathery from all the slaps he's gotten, while the left is soft. This is backwards - anyone hitting him with their right hand would hit his left cheek.
Incel: Who are they?
Sherlock: That's Homeland Security.
Incel: But...you promised you wouldn't tell them about me if I talked to you!
Sherlock: Yes, but you play den mother to a pack of would-be rapists and mass shooters, so you can see how lying to you would be the highlight of my day. Look on the bright side - you don't seem to enjoy the company of women, and that shouldn't be a problem for the next five to ten years.
The Hound of the Cancer Cells - S2-E18
Trivia: "The Hound of the Cancer Cells" is a loose reference to "The Hound of the Baskervilles", perhaps the most famous of the four Sherlock Holmes novels.
The Rat Race - S1-E4
Question: I don't see her listed on the credits in beginning or any other website inquiries, but is that Tyne Daly playing the character Peter's secretary?
Answer: I'm the same person who asked this question. I discovered it was Molly Price whom I recognized from Third Watch.
Cathrine R
It should be noted Donna was Jim Fowkes‘ secretary. Donna killed Peter.
Bishop73