Continuity mistake: 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.
Continuity mistake: Sherlock and Watson are riding in a limousine. They are seated on the back-facing seats of the limo. Thee are 2 passengers seating on the back seats. The street background visible through the back and side windows shows traffic and the limo moving forward. Some shots of Sherlock show the background traffic moving in the right direction (backwards) and one shot shows traffic moving in the opposite direction, as if Sherlock was seating on the back seat or the limo was moving In reverse.
Continuity mistake: When Marcus and Joan are watching Gephardt's video, he says he's taken lives. At this point the play bar is by his fingers. It cuts to Marcus and Joan, and we hear the video continue to play for more than 12 seconds. When it cuts back to the video, the play bar is nearly in the same position, when it should be well past his hands and near his elbow.
Continuity mistake: When Shinwell and Sherlock are playing chess, the captured pieces move around in various shots. For example, Shinwell takes Sherlock's knight, he places it closer to him than the pawn. In the next shot the pawn is closer to him. It changes a few more times as do the captured white pieces.
Continuity mistake: The note Watson picks up changes when it switches to a close up view of the writing. For example, you can see one line ends with "you when" and another line ends with "not" (being underlined). In the close up the corresponding lines end with "you when I" and "not to" (not still being underlined).
Continuity mistake: When Joan is sitting on the couch folding ties while Shinwell tries on a shirt, she has a folded up blue tie with white dots. When the camera cuts back to her and she's now folding a gray tie, you can see the blue tie with white dots, unfolded, lying on the clothes. Previously there was no tie there. And in the next shot of her, she once again folding the blue tie and the gray tie can't be seen.
Continuity mistake: In the title sequence a Rube Goldberg machine can be seen. The error can be seen by watching the four revolvers rotating and then a single revolver firing. When you look at all four revolvers, there are hand grips in each one, but in the closeup shot of one actually firing, the hand grip is empty.
Continuity mistake: When Joan accuses Agent Whitlock of gathering intel to rip off/ambush/rob the gangs, a woman enters the hall behind her. Moments later, the woman disappears having never walked past Joan or Agent Whitlock. She didn't open any of the doors in the hallway either since she was walking straight down the hallway.
Continuity mistake: While talking Paige picks up a small white Chinese food takeout container to close it and puts it back down on the desk. She picks up a the larger container that has the red pictures and the word enjoy on it and starts to close it. In the closeup she has the small white container back in her hand.
Continuity mistake: When Sherlock first accuses Irene of working for Moriarty, he pins her to a bookcase. When she shoves him away and breaks free, her hair ends up arranged with some strands in front of her. During the following minute, those strands repeatedly switch back and forth from behind her shoulders to in front of them.
Continuity mistake: While Joan and Sherlock are chatting, Joan is trying to make peanut butter and jelly sandwiches, but the shots alternate between the two and Joan repeats her movements, wipes the peanut butter over and over on the bread, and changes her mind with the jelly bread.
Continuity mistake: The brownstone has two front doors, an outer door and an inner door. In scenes before this one and after this one, the outer door is made of wood and the inner door has a large glass panel, at the top, but in this episode the outer door has a large glass panel, at the top, so they can see who it is before opening the door.
Continuity mistake: When Detective Bell receives a phone call from Gregson in Holmes' house, he rushes upstairs and bangs on the bathroom door - Sherlock is inside, he said he wanted a shower. Bell rattles the handle, but finds the door locked, so he kicks the door in. But Sherlock didn't lock the door. The lock is above the handle and Sherlock did not use it.