Castiel and Cain in “Unfinished Business”

Castiel

This is a massacre.

Cain

Yes. And soon it will be a genocide. My children, my whole poisoned issue. Lot of them out there right now... killers, fighters, thieves. Some more peaceful than others, but they still carry it... the disease. If the Mark wants blood, I'll give it mine.

Castiel

You are Adam and Eve's first born, your descendants are legion.

Cain

At most I'm culling... one in ten.

Castiel

Of everyone.

Cain

I've got time.