Yeah, it's not entirely clear... maybe he was thinking "hey, I have an idea, let's throw in an Arthurian reference!".

That is a good line. Though it's part of a somewhat unfortunate tendency in modern times to interpret "chivalry" as purely "men being gallant to women". It was rather broader than that in its Arthurian sense.

Ironically, considering your comment about the rook thing coming out of nowhere, you have indeed forgotten something: Ron literally sacrificing himself in the magic chess game all the way back in book one. But it's true it's rare for him to take much initiative in the heroics.

So it is. Much of it is plausible, really, to an insecure mind - that's why it's so nasty.

Yeah, I agree, it's a good scene - shows real emotional depth. Hermione is not a very nice person when she's angry, so it's a good thing she doesn't get angry without good cause.

And in the magical equivalent of the Holy Grail. Can you tell I'm seeing Arthuriana everywhere now? As a poke at Dan Brown and his readers, this would be rather well hidden (no, I don't really think it was intended as such), but accurate.

Interestingly, she doesn't seem to resent Hermione, who's rarely been all that warm to her.