The famous “It should have been you” scene. The “stupid decisions” Catelyn haters rant on about (e.g., abducting Tyrion) are mostly not that stupid when considered in context (certainly no stupider than many of Ned’s). But Catelyn’s behavior toward Jon really is hard to excuse.
In response, Jon continues his record of hiding his negative feelings, “[forcing] himself to smile” in the face of Robb’s inane comments about the Night’s Watch (as if the shift to an all-black were the biggest life change Jon had coming), and telling Robb that Catelyn was “very kind” to him. (Meanwhile, Robb is now “shouting commands with the best of them” and “seems to have grown” in the face of hardship — though not enough to prevent him from deluding himself that this assessment of Catelyn as true, when the fact that he asked Jon about Catelyn’s behavior to begin with shows that he knows, deep down, it isn’t.)
As before, Jon does let the mask slip a bit when he’s with Arya, defying authority by giving her a sword (how did he get Mikken to make it? by saying he wanted it for himself?) and encouraging her to hide it from Septa Mordane and Sansa. (As a bonus, we learn in this scene that Westerosi women, or at least the ones Jon and Arya are familiar with, don’t shave their legs.)
Finally, a bit of potential, still-unfulfilled foreshadowing: “Different roads [Jon’s and Arya’s] sometimes lead to the same castle. Who knows?”