DOCTOR: To the rational mind, nothing is inexplicable; only unexplained.

LEELA: Doctor, why didn't the helium make your voice go squeaky?

DOCTOR: Because I'm a Time Lord. I've been around, you know. Two hearts, respiratory bypass system. I haven't lived seven hundred and fifty years without learning something.

DOCTOR: You know, you're a classic example of the inverse ratio between the size of the mouth and the size of the brain.

(D84 reaches the communicator.)

D84: Goodbye, my friend.

(D84 turns it on, and his head explodes)

UVANOV: I suppose it's also a coincidence that as soon as you two arrive, three of our people are killed? (pause) Well?

DOCTOR: Oh, sorry, I thought it was a rhetorical... well, yes, it's just a coincidence.

LEELA: You mean you can't control this machine?

DOCTOR: Well, of course I can control it! Nine times out of ten. Well, seven times out of ten. Five times— look, never mind, let's see where we are.