Sometime later the conversation has morphed from Sophie inviting him to shut Craig up into actually confiding in the Doctor, just like people always do. And by a stroke of luck, she's happened on his favorite subject: The indomitable human soul and free will and not being boring: "Because life can seem pointless, Doctor. Work, weekend, work, weekend. And there's six billion people on the planet doing pretty much the same." The Doctor mumbles to himself that watching the Craig & Sophie glacial mating dance makes him wonder where all those folks even came from, and then changes the subject before they can nail him on it.
"So, the call center. That's no good? What do you really want to do?" Work with animals. Like there was this orangutan sanctuary on telly that she loved, but -- as Craig almost smugly points out -- she's unqualified for that work. Just when you think it's going to some kind of dark codependent place where Craig might be subtly keeping her down, Sophie brings up the time Craig also refused a job elsewhere, in London. "I can't see the point of London!" he says. The Doctor has sort of had enough.
"Perhaps you'll just have to stay here, secure and a little bit miserable until the day you drop. Better than trying and failing, eh? Everybody's got dreams, Sophie, very few are going to achieve them, so why pretend? Perhaps, in the whole universe, a call center is where you should be?" Sophie is horrified, and with just a little prodding spits it out: "I'm not staying in a call center all my life, I can do anything I want!" He turns on her the most gorgeous, shining grin that ever crept across a face, and Sophie has herself a genuine moment. "Oh, yeah! Right, oh my God! Did you see what he just did?" Craig's like, "Um, you're going to live with monkeys now?"
The Doctor isn't letting them off that easy: "Big old world, Sophie. Work out what's really keeping you here, eh?" They are glum, and stare into space for a bit, before Craig asks the question again, hoping for a better answer... But she has no option but to agree, that there's nothing really keeping her in Essex, because at this point neither of them can actually call the bluff. The Doctor is like, "Good Lord."