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 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: 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.
Factual error: In the scene in the hospital, the guy who drove his motorbike into a van has an IV canula in his right hand, but the IV pole and the IV bag are on the left side of the bed, which means the IV line has to be long enough to go up to the bedhead, then behind the bedhead and then up to the bag, leaving no way to check for air bubbles.
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.