Jack purred into the kiss, pulling back only just enough. "You're happy," he grinned against Ianto's lips.

"No fair guessing," Ianto smirked.

"It's not a guess, you can't hide it, not even if you wanted to," Jack said smugly.

"Oh, I could, if I wanted to. As it goes, doesn't make much sense I'd try hiding it while you're snogging me, does it?"

"That's just it. That's exactly when you can't hide it."

Ianto sat back a bit, giving Jack a look. "What are you on about?" he asked, though he knew he should be used to Jack's nonsense.

Jack glanced away, realizing he'd let something slip, but finding he didn't really mind the idea of telling Ianto. "Well… it's not exactly a secret, I guess. Just kinda one of those weird evolutionary things that I don't usually tell people about. See, I, uh, can kinda taste how you're feeling. In a kiss, I mean."

"Are you serious?"

"Yes," Jack said carefully, watching Ianto's eyes.

"What's that like, then?" Ianto asked after a moment to process it. "I mean… is it like, I taste like Victoria sponge when I'm happy, but anchovies when I've not had a good day?"

Jack laughed at that notion. "Of course not. It'd be more like different kinds of tea. You know it's all tea, but there's a definite difference between a Darjeeling and a Lapsang souchong."

"Oh, I get you."

"It's not always that obvious, of course. There are a lot of subtleties in emotion. But I can clearly tell when you're particularly happy or… not. Of course, kissing generally increases endorphin and serotonin levels, so that alone changes the taste even if you're feeling a bit blue. Happiness just sort of… brightens the taste. No other way to describe it."

"Out of pure curiosity, what does it taste like when I'm seriously annoyed with you?" Ianto asked.

Jack chuckled. "Like the darkest chocolate. Almost too bitter… but… captivating, as well."

"That explains it," Ianto nodded.

"Explains what?" Jack said, wondering if he'd missed part of the conversation.

"Why you always seem to think a snog will fix it when you've done, or not done, something to annoy me," Ianto smirked.