Alien threats. [Just when he'd thought he had heard it all in this place. Here was something new. Well, new-ish. He now knew that aliens did exist for a fact and had even met someone from a different world than Earth. But the words alien and threat in the same sentence was a new one.]
[He smirks and files the name Ianto away for later.] I don't guess you could expand on that... alien threats.