Snape's growing familiarity with Al certainly hadn't meant Al had lost that unique capacity of his, to be an endless source of surprise. Just when I thought I couldn't really be surprised by anyone; I'm surprised on an ongoing basis, by the same someone.
Serves me right for thinking I've seen and heard it all. Snape concluded wryly.
Al's comment about dessert, which would have been arrant flippancy from anyone else, and was somehow simple honesty from him, startled a voiceless huff from Snape. "Completely," he agreed wryly.
He inclined his head. "I'd be honoured to attend," he declared gravely, before a spark of dry amusement broke through. "Do you have any idea what changed Harry's mind? What are the chances I'll be the main course on the dinner menu? Spitroasted or charbroiled?" he smirked.