At the beginning we see a masked man shooting two people with their faces covered with pillows. When he shoots the first victim the mask gets splattered with blood, but a second later, when shooting the second victim the mask is completely white and there is no blood splatter anymore.
When Watson sits down to talk to Sherlock at the beginning of the episode, she sets down her smoothie to her left. When the camera cuts to Sherlock the glass is next to him, but when the camera cuts to Watson, it is next to her. When Sherlock gets up, he does not take the glass, but Watson drinks from it indicating it is her glass that mysteriously moves between takes.
Sherlock says Juan has bright blue eyes, like his father, but Sean's eyes are brown.
While reviewing police interviews from the 1990s Holmes is using a modern flat-screen with 16:9 aspect, yet the old videos fill the screen without distortion. Police interview rooms wouldnot have been equipped with widescreen cameras in the '90s.