"I do know my way around a milkshake," Prompto admitted proudly, "and a trap. You girls don't even know what you've gotten yourselves into by opening the door to that one."

Though this was hardly the sort of booby trap any of them likely had in mind. His grin faltered a little, though, letting her enjoy at least some of that milkshake before diving into anything, or perhaps just letting her drink up some of it now so that there was less that was likely to wind up in his face later.

That was a possible outcome that was only just now coming to his mind and he was starting to wish he'd worn a shirt he'd be a little less heartbroken about being ruined by a milkshake, and then realized, after the Ketchup Catastrophe, that food and Nina and his room were not a wise combination that should probably be avoided in the future if things did turn out that way.

"I must confess, though," he informed her, "that this milkshake absolutely does have an ulterior motive."

Which he'll get to. He was....building suspense. Or just delaying things. A little of both, but mostly the latter, definitely mostly the latter.