Continuity mistake: During the party, Stass the assassin, dressed as a waiter, hides his gun underneath a stack of white napkins. When he gets ready to pull the gun out, it is now between the napkins.
Continuity mistake: In the opening scene when John is going to the refrigerator, a white skull can be seen on the left side of the kitchen table amongst all Sherlock's science equipment. When he closes the refrigerator door again after discovering the severed head, the skull has disappeared. As he's leaving the kitchen, the skull reappears. (00:03:25)
She Works Hard for the Money - S1-E4
Continuity mistake: Jane shows the photo of the victim Danielle to her old contact. She holds the photo differently, either above its left corner or below it. (00:22:15)