DOCTOR: Maybe we opened the prison but not the cell.

IDA: We should go down. I'd go. What about you?

DOCTOR: Oh. Oh, in a second, but then again, that is so human. Where angels fear to tread. Even now, standing on the edge. It's that feeling you get, eh? Right at the back of your head. That impulse. That strange little impulse. That mad little voice saying, go on. Go on. Go on. Go over. Go on. Maybe it's relying on that. For once in my life, Officer Scott, I'm going to say retreat. Oh, now I know I'm getting old.