Sam and Dean in “Unfinished Business”

Sam

You think I'll do it, don't you? You think I'll go darkside.

Dean

Yes! Okay? Yes. The way you've been acting lately! The things you've been doing! Oh, I know. How you ripped Alistair apart like it was nothing, like you were swatting a fly. Cas told me, okay?

Sam

...What else did he tell you?

Dean

Nothing I don't already know. That you've been using your psychic crap and you've been getting stronger; we just don't know why and we don't know how.

Sam

It's not what you think...

Dean

Then what is it, Sam?! 'Cause I'm at a total loss!