Demons make promises. Present offers. Tempt. Cullen knows he can't do any of those things.

Alistair pokes him; he laughs, quietly, unable to stop himself. But that's all.

(Alistair didn't respond to the offer of cheese -- itself a temptation, he supposes -- but if he had to guess how Alistair Theirin might try to figure out whether someone in front of him was a demon... starting with a cautious poke is utterly Alistair.)