In which the Doctor does.....nothing

The Doctor: Biroc! What are you doing here?
Biroc: Nothing.
The Doctor: It's all right for you.
Biroc: And for you too. Do nothing.
The Doctor: Do nothing?
Romana: Of course. Doctor, don't you see?
The Doctor: Yes that's right. Do nothing - if it's the right sort of nothing.

( Planet of the Ood (contains spoilers) )