The Doctor and The Nucleus in “The Invisible Enemy”

[finding something strange in his brain] Who are you?

I am the Nucleus.

You're trespassing, you know. Treading on my unconscious, affecting my metabol... Nucleus of what?

The Nucleus of the Swarm.

Oh. Oh, I see. Why did you choose my brain?

Because of your intelligence.

Oh well, I can understand that, but you realise you have no right-

I have every right! It is the right of every creature across the universe to survive, multiply and perpetuate its species. How else does the predator exist? We are all predators, Doctor. We kill, we devour to live! Survival is all, you agree?

Oh yes, I do, I do. And on your argument - I have the perfect right to dispose of you.