Ok, I've watched the episode a few times now, and gone back to "The Incident" to take special note of Jack's neck (I know, odd thing to watch the entire time!), but I can't figure out the cut.
He pays special attention to it in the bathroom, and we're obviously supposed to notice it.
Now, is there something significant about it that I missed? How did he get it? Why is it important?
Or do we just not know yet?