Oh my gosh you guys I just realized that when Melody asked who River is, the Doctor says "Spoilers" because he's remembering all those other times he met River, but that's the first time she meets him, so all those times she says "spoilers" she's quoting him, and all those times he says "spoilers" he's quoting her!!!! <-- Mind. Blown.
Dalek: Records indicate you will show mercy. You are an associate of the Doctor's. River Song: I'm River Song. Check your records again. Dalek: Mercy? River Song: Say it again? Dalek: Mercy!! River Song: One. More. Time. Dalek: Mercy!!!!!