On the scene between the Doctor and Clara immediately after the volcano in Dark Water:
I loved the scene. The acting is extraordinary and that is what I think has powered this series. I’m also proud of a line – I’m very rarely proud of anything I write – but I’m proud of the line ‘Do you think I care for you so little that betraying me would make a difference?’ because I got obsessed when I started to write this that Cybermen have no emotion, so it starts with Clara unable to find a way to say I love you and ends with Danny unable to find a way to say I love you, there are two phone calls that book-end it, and in the middle, the cracked old Caledonian gets it exactly right, he says I love you perfectly. […]
He’s surprised he has to say it. That’s the truth about him, he says lots of horrible things all the time, that’s because he assumes all the other stuff is taken for granted and it’s only in that moment Clara realises just how much he’s assuming is taken for granted, absolute monomaniacal devotion to her. He absolutely loves her.
Steven Moffat, Doctor Who: Anatomy of a Hit (x