It wasn't a particularly long or deep kiss. Really, it was just a brief smack on the lips, not unlike the pecks on the cheek or hugs Penny was prone to giving Leonard and Raj (never Howard), merely a somewhat more enthusiastic display of affection in her jubilant state. It couldn't have been longer than one Mississippi, tops. She simply grabbed the sides of Sheldon's face from where she sat beside him on the couch, kissed him with a resounding "Mmmwa!" and released him.

He was paralyzed.

Penny giggled at his stunned expression, eyeing him as though half amused, half waiting for an explosion.

"Sorry, Moonpie, I forgot you detest all forms of physical contact." She laughed, wiping her lip gloss off his bottom lip with her thumb. Then she turned back to her present, gushing over the colour, eager to try it out, clearly thinking nothing of what she had done.

And still Sheldon sat, paralyzed.

Used to odd behaviour from the scientist, no one seemed to notice anything was amiss, with only a brief exchange between Penny and Leonard of,

"Penny, I think you broke him."

"He'll survive. Pass me the power cord."

They had no idea how apt Leonard's statement was. Sheldon's brain was overloaded with racing thoughts. Thoughts of germs, warm hands, infectious diseases, soft lips, Vulcan's, blonde hair, the scent of vanilla, the taste of strawberry lipgloss, homo novus – those and more whipped through his mind like particles in a collider. He didn't dare move, for much like particles in a collider, Sheldon's thoughts were threatening to burst within him.

It took every effort when he finally did risk movement, to quietly excuse himself, stand carefully, and walk even more carefully from the couch to his bedroom, where he quietly shut the door. He heard Penny remark from the living room with a note of fondness,

"Probably gone to find some high power mouth wash. Poor whackadoodle."

Sheldon had hoped retreating to the safety of his bedroom would provide relief of this feeling now overwhelming him. Instead, in the relative silence, it allowed his thoughts to race even more freely. He moved slowly to his bed, laying down in his usual sleeping position, but on top of the covers. He stared unseeing at the ceiling, willing some semblance of calm to wash over him and quiet his mind.

Sheldon thrived on consistency. He did not take well to being blindsided, to say the least. He had felt a hint of this indefinable reaction the few times he had happened to touch Penny. There had been the first day they met – even before touching her, he had been unexpectedly delighted when she appeared impressed by his equations, and had even felt the need to impress her further, (though only momentarily of course). That same day, he lost his pants to her ape of an ex-boyfriend Kurt when Leonard left him no choice but to go along on the useless venture to retrieve Penny's television. It was Penny who was so beholden then that she had embraced Sheldon and Leonard in thanks for their efforts. Much like the kiss, that too had been only a brief moment of contact. But a sensation had run through him so strange that he found himself instinctively turning his body away from Penny. And it had been a total of three times now when he had been so moved by appreciation towards Penny that he had put his arms around her before he could stop himself, and a whisper of that same sensation had afflicted him when he did so. He had dismissed all these instances as isolated and anomalous, due to various states of stress or euphoria and unlikely to occur again.

But now that. That had happened and this time he couldn't simply shrug it off. It was more than his fear of germs. He'd fallen ill twice now due to being close with Penny and had mostly conquered that particular anxiety, though it was still a minor concern. What was truly horrifying was his body's reaction to any form of physical contact with Penny. He had believed himself above the need for animalistic tendencies and his body's base instincts. Like a Vulcan, Sheldon prided himself on being above such ugly attributes as emotion, desire, and sexual attraction. But from the moment he had met Penny, he had been forced to acknowledge and face aspects of himself he had been convinced did not exist. He should've known something like this would happen. Penny was always introducing new and unpleasant things into his life. Not that the feeling itself was entirely unpleasant but the anxiety it provoked certainly was. Sheldon didn't know how to conduct himself when it came to even the idea of attraction. It was akin to being naked in public; it left him feeling very exposed. He'd managed to avoid it his whole life, up until meeting Penny. With her living next door, however, avoidance was out of the question. It didn't help that Penny seemed insistent on forcing her way into his every day. He did his best to be cold, rude and even downright insulting towards her, but that only seemed to make her more determined to be friends with him. Her very presence was an assault against his defences, and that simple kiss had nearly brought them crumbling to he ground.

For once in his life, Sheldon didn't have an answer...