Lyall's smile turns just a little more amused at the understanding. Well, it had been his intention. Not exactly a test but something of a game that he is pleased Aziraphale has successfully played.

"Yes, well, I can't say that they do not exist." A pause, and then with a slight nod of his head. "That we do not, that is."

He could make the information more of a challenge but he would rather observe Aziraphale's reaction to it.