The title of this episode is a direct quote from the books. Arya Stark refers to herself as "The Ghost of Harrenhal" in "A Clash of Kings", Chapter 30.
Jorah Mormont: (to Daenerys) There are times when I look at you and I still can't believe you're real.
Jaqen H'ghar: A man pays his debts. A man owes three.
Arya Stark: Three what?
Jaqen H'ghar: The Red God takes what is his, my lovely girl. And only death may pay for life. You saved me and the two I was with. You stole three deaths from the Red God. We have to give them back. Speak three names and a man will do the rest. Three lives I will give you, no more, no less. And we're done.
Arya Stark: I can name anyone? And you'll kill him?
Jaqen H'ghar: A man has said.
Tywin Lannister: And what do they say of Robb Stark in the North?
Arya Stark: They call him the Young Wolf.
Tywin Lannister: And?
Arya Stark: They say he rides into battle on the back of a giant direwolf. They say he can turn into a wolf himself when he wants. They say he can't be killed.
Tywin Lannister: And do you believe them?
Arya Stark: No, my lord. Anyone can be killed.
Tyrion Lannister: (about Joffrey Baratheon) The king is a lost cause. It's the rest of us I'm worried about now.
Margaery Tyrell: (about Renly) He was very handsome.
Petyr Baelish: He was, Your Grace.
Margaery Tyrell: Your Grace? Calling yourself king doesn't make you one, and if Renly wasn't a king, I wasn't a queen.
Petyr Baelish: Do you want to be a queen?
Margaery Tyrell: No, I want to be the queen.
The episode won an Emmy Award for Outstanding Art Direction for a Single-Camera Series.