That Forgotten Wednesday

*Season 3 Spoilers* Prompted by part of Sherlock's speech in The Sign of Three. "As a mental exercise, I've often planned the murder of friends and colleagues. Now, John I'd poison. Sloppy eater. Dead easy. I've given him chemicals and compounds that way. He missed a whole Wednesday once, didn't have a clue." John may not remember that Wednesday, but Sherlock does. Johnlock