The Stones of Blood

DOCTOR: Here. Look, how can I explain? Listen, Einstein's Special Theory of Relativity said

EMILIA: Said that you cannot travel in space faster than the speed of light, because the speed of light is a limiting factor. If you travelled more than a hundred and eighty thousand miles per second, you'd encounter the time distortion effect.

DOCTOR: Yes. Yes, well, he was nearly right.

EMILIA: In fact, you'd arrive at your destination before you'd left your starting point.

DOCTOR: Yes. Absurd, isn't it?

EMILIA: Oh, I don't know.

DOCTOR: I always thought it was fun, myself. I did try to explain the realities to poor old Albert, but he would insist that he knew best.

EMILIA: Oh, they're all the same, these physicists. Oh, sorry.

ROMANA: K9, what is tennis?

K9: Real, lawn or table, mistress?

ROMANA: Never mind. Forget it.

K9: Forget. Erase memory banks concerning tennis. Memory erased.