I was re watching Sign of Three a bit ago & noticed 2 mistakes.
1. When Sherlock drops the glass during his toast... The special effects crew forgot to blend out the brown patch on Sherlocks wrist that was meant to catch the sound of the glass leaving his hands.
2. The part where Sherlock & John run after Major Shoto . they didn't take out the back of Mary's dress chasing after John, before cutting back to her sitting down. Whoops edit team.