Continuity mistake: As Sherlock and Watson come out of their apartment to hail a taxi to be taken to Brixton and the scene of a murder, two extras can be seen in the shot - one crossing the road and one walking up the far side of the street. At the top of the street there are two white colored cars, but they suddenly disappear, to be replaced by a dark colored car. Also the light of the building across the road is suddenly turned on.
Charlie McGee
2nd Jan 2016