SARAH: It's weird seeing London like this. All those deserted streets.

YATES: I rather like it.

YATES: Have you noticed the air?

SARAH: Hmm?

YATES: It's clean. No cars, no people. Do you know yesterday I saw a fox in Piccadilly?

SARAH: And nightingales in Berkeley Square?

YATES: It's not impossible.

SARAH: No. No, I like London the way it was, traffic jams and all.

YATES: Yes, I expect you're right.

BRIGADIER: The man was mad.

DOCTOR: Yes, well, of course he was mad. But at least he realised the dangers this planet of yours is in, Brigadier. The danger of it becoming one vast garbage dump inhabited only by rats.

BRIGADIER: It’ll never happen, Doctor.

DOCTOR: It’s not the oil and the filth and the poisonous chemicals that are the real cause of pollution, Brigadier. It’s simply greed.