(Nancy hugs Jamie and a cloud of nanogenes surround them.)

ROSE: What's happening? Doctor, it's changing her, we should—

DOCTOR: Shush! Come on, please. Come on, you clever little nanogenes. Figure it out! The mother, she's the mother. It's got to be enough information. Figure it out.

ROSE: What's happening?

DOCTOR: See? Recognising the same DNA.

(Jamie lets go and Nancy falls on the ground.)

DOCTOR: Oh, come on. Give me a day like this. Give me this one.

(The Doctor removes Jamie's gas mask.)

DOCTOR: Ha-ha! Welcome back! Twenty years till pop music – you're gonna love it.

NANCY: What happened?

DOCTOR: The nanogenes recognised the superior information, the parent DNA. They didn't change you because you changed them! Ha-ha! Mother knows best!