There is an inconsistency in the Reichenbach Fall episode, and I can't figure out if it's a mistake by the writers or deliberate.  Near the end of the episode, in St. Bartholemew's Hospital, when Sherlock and Watson are trying to figure out where Moriarty's key code is, Sherlock tells Watson that Moriarty didn't touch anything in 221B Baker Street except the apple.  But it struck me immediately that when he visited Sherlock (the tea scene) he also touched the knife with which he carved the apple.  In fact, it was still sticking in the apple and Sherlock used the knife to pick it up.  How could Sherlock miss that, when he catches the minutest details normally?  Did Sherlock (and the writers) mean that the knife wasn't important? Or was this the un-Sherlock-like moment, and it was really misdirection on Sherlock's part? Or just a mistake on the part of the writers?

I went back to see where the knife came from.  You never see where Moriarty got it; it just appears in his hand right before he sits down.  There isn't any point where he is shown picking it up, or taking it out of his coat; it just appears.  Not sure if we're supposed to infer that he picked it up or that he brought it with him, but I don't see any opportunity for him to pick it up.  At the same time, a knife very like it shows up near the beginning of episode 1, first season, where Sherlock sticks it in the mantelpiece, so maybe it's supposed to be the same one and it was in the apartment already.  Of course, Moriarty did touch it, so maybe he planted a key code in it??

That would mean in the final confrontation between Sherlock and Moriarty that Sherlock knew the key code existed and was playing ignorant so he could use the key code later, perhaps to help fake his death (although it wouldn't help him survive the Fall, obviously).  What's puzzling me the most is that the episode seems to go out of its way to deny the existence of Moriarty's key code.  When Moriarty denies its existence in their final confrontation, he could simply be doing it to keep Sherlock trapped into committing suicide, but as Moriarty explains how all his break-ins were accomplished, we see images of the break-ins that corroborate what he's saying.  Always before in the show, such scenes have been things that really happened, not fake.  And why would Moriarty use conventional means to make it look like he had a key code, if he really had one?  And a key code like that really is impossible.  There's nothing that all computer programs have in common that could be exploited like that.  On the other hand, upon re-re-re-rewatching the episode, I notice that Mycroft thinks the code is real, so maybe it is, or maybe he and the international spies have all been fooled.

In sum, I can't tell if we're supposed to think the key code's real or not.  On the one hand, it certainly makes a good un-Sherlock-like moment for Sherlock to have been fooled into thinking that the key code existed, but that doesn't help explain how he faked his death.  On the other hand, it's really un-Sherlock-like to miss the knife, so I think he's just pretending to be surprised to fool Moriarty into thinking he was convinced the key code didn't exist, so he can go back (after "death") to fetch it.  He probably didn't have it when he told John they needed to go back and find it, so he couldn't have used it to help fake his death before the Fall, and it certainly wouldn't have helped him during the Fall, but he could have used it to cover his tracks afterward.  And maybe it will provide the reason Sherlock stays undercover, until he could go back and get it.

(Another really good candidate for the un-Sherlock-like moment was when Sherlock begged Moriarty for (and got) a moment of privacy.  I suspect he took some drug then.)

So, who missed the knife - Sherlock or the writers?  And if Sherlock "missed" the knife, what might it mean?  Any deductions, anyone?