Disclaimer: The Big Bang Theory characters are (c) Chuck Lorre and Bill Prady.

Author's Note: Of course, more Sheldon/Penny. How could I not? (&LeonardOC)

The Concept of Breathing by Mika Casey

"Penny, I'm afraid of the dark."

The blonde woman heard Sheldon's voice through her doorway, because after his nine knocks and three mutterings of her name she still didn't open the door. It was 2:17 A.M. according to Penny's cell phone, and she had already been awake playing Age of Conan because she couldn't fall asleep. And she knew that Sheldon had been awake, because her virtual player had conversed with his a few minutes ago. But now, Sheldon was away from his keyboard and knocking on her door, trying to gain access.

She snorted, subconciously fiddling with the strap on her lavender nightgown. "Honey, there's no way you're afraid of the dark. You're Sheldon Cooper, you find logic and reason in everything around you." Which was why he didn't understand sarcasm, and why Penny and the boys couldn't take him out on Halloween night, because he believed nobody could possibly be wearing such riddiculous masks, so hence he thought that aliens and monsters were invading the Earth.

He sniffed, and she could imagine him rolling his bright blue eyes. "Leonard's not home! He's out partying with Raj and Howard. And sometimes I sleep so deeply that I wouldn't be able to tell if a murderer crashed through my window and were going to come in to my room and strangle me!" There was obvious distress in his voice.

Yawning, Penny finally gave in and opened the door. She smiled when she saw that he had a sleeping bag and pillow in his arms, and was wearing his two-piece Spiderman pajamas. He started babbling. "Is it socially acceptable for me to come into your room, Penny, especially at this time of night? Because I know you're a female, but you are also a good friend of mine and I don't want to impose..."

"Of course it's okay, sweetie." Penny told him firmly, and she watched as he sighed in relief and unrolled his sleeping bag before placing his pillow at the opening. "Would you like some tea?" She asked.

Sheldon, who was now sitting cross-legged on his sleeping bag, looked up at her with a tired half-smile on his face. "Yes, please."

Penny rustled about in the kitchen in attempt to put the water on the stove and find Sheldon's favorite coffee mug. This was the fifth time that Sheldon had slept on a sleeping bag on her floor in the past month, and she was getting used to it.

The tea kettle began to whistle like a train departing from its destination, and Penny poured the water into Sheldon't mug before lowering his favorite tea bag into the liquid. She let it sit on the counter, stirring it occasionally, and when the flavor was thoroughly soaked through the water she extracted the bag and carried the steaming cup to her guest with both hands.

She entered the room, and saw him sitting on the floor with his back leaning against her couch. His eyes rolled so he could look at her, and he spoke. "Thank you, Queen Penelope."

"You're welcome, Sheldor."

Sheldon hated hot days.

He was sitting on his favorite sofa cushion in his apartment with Penny's leaning into his lap and chatting about their latest adventures in online gaming, because Leonard was out with Leslie and Howard at a water park to cool off. Penny had opted not to go because her body "was not bikini ready", as she put it.

But Sheldon definitely didn't agree. She was wearing a pair of short green-plaid boxers and a tight white shirt that exposed most of her stomach while holding an almost empty glass of ice water in her hand, and Sheldon could not find any excess fat anywhere. Something posessed him to press his fingertips against her flat stomach, and felt her muscles clench as her body spasmed and she instinctively brought her hand down over Sheldon's hand.

"What do you think you're doing?" She asked, mouth agape.

Looking at her confusedly, Sheldon spoke. "Penny, most women say that their bodies are 'not bikini ready' when they have extra fat under their skin. There is none to be found here." He told her matter-of-factly, spreading out his fingers so most of his hand was covering her stomach.

Penny shifted so she was out of Sheldon's lap and his hand fell away from her stomach. "Sheldon, there's a lot you don't know about how a woman feels for her body."

Sheldon's eyes twitched. "Don't know?" He laughed. "I know plenty! I am very aware that your height by weight ratio is perfect for your body shape, and that you have an ideal body that is very attractive to men."

Deadpanning, Penny blinked. "Um...how do you know that, Sheldon?"

"Uh..." Sheldon realized what he just said. His eyes flitted from her to his hands, and back to her when he gave a final answer. "Leonard's behavior. Yes, of course. He's quite attracted to you, as you know."

"Sheldon, Leonard has a girlfriend." A redhead, freckled girl named Tracy who lived on the first story of their apartment complex and had a PhD in subatomic physics.

Correcting himself, Sheldon stuttered. "W-was. Was attracted to you. And its not like I haven't made my own assumptions about your body." He added, trying to remain nonchalant. The heat was starting to get to him, causing a bead of sweat to trickle from his hairline and over his cheek like a hot tear. He brought his hand up to wipe the moisture away.

"Mm-hm." Penny muttered, smiling coyly. "So the great Sheldon actually likes women. I had my doubts." She chuckled.

Sheldon was immediately on the defensive. "Of course I am attracted to women! Its part of my nature as a heterosexual human being." He huffed.

Penny excused herself to renew her glass of ice water in the kitchen, and to avoid the rest of the conversation.

Penny loved watching stars dance across the sky.

On this occasion, she was lying back on a plaid quilted blanket with Sheldon, Leonard, and Leonard's girlfriend Tracy, and the three others were pointing out differently constellations that glittered in the night. They were in a stretch of grass in the back of the apartment complex, awaiting the arrival of a meteor shower. Penny was in her fluffiest pajama bottoms and longsleeve top to keep out the cold, her hair was a mess sitting on top of her head in a messy bun, and she wasn't wearing any makeup.

Leonard excused himself and Tracy, claiming that they were both too cold to stay outside and watch the meteor shower. It was obviously planned, because Leonard knew that Sheldon would not remove himself from that blanket until the last meteor streaked across the sky.

Clever. Penny thought. They get a little alone time up at Leonard's apartment.

The two bade Sheldon and Penny goodnight, and crept back to the complex. Sheldon immediately began talking, pointing out various stars and planets above their heads.

"And you see that celestial body, Penny? That's Venus." He said, smiling his little half-grin. "Named after the goddess of beauty." Turning from his position lying down next to her, he watched her. "You would be a phenomenal representation of the fictional goddess."

Penny caught her breath, confused and unsure what to say. Eventually, she spoke quietly. "Sheldon, did you just call me beautiful?" She asked, unsure whether to smile or frown. "Because if you're testing out sarcasm, this isn't exacly the best time..."

"No, I'm not being facetious." He interrupted her. "You are beautiful. Your hair is like rays of sun when the light hits it right, and your eyes..." He hesitated, blinking. "...well, your eyes are bright and perfectly shaped. They're almost stars themselves."

Penny knew that Sheldon only stated facts that were not neccisarily based on his opinion, so this admission could mean absolutely nothing at all.

But she didn't want it to mean nothing.

Adjusting herself so she was sitting half-upright and leaning over him, Penny looked into his eyes. They were dancing with flecks of blue, reflecting the stars that were lying behind her head. Her hair fell over her shoulders and onto his Green Lantern tee-shirt, and she put one arm over his body so she was balanced above him. Without saying a word, she dropped her face so their lips met. She felt his shock as his whole body went rigid.

As she was about to pull away and apologize, she felt Sheldon's lips melt against hers. It reminded her of her first kiss, her freshman year of high school, how jumbled and desperate and overwhemingly their mouths moved against each other. Sheldon's hands came up to her face, covering her cheeks with his long fingers and not letting her mouth leave his. Although Penny could tell he was lost and had no idea what he was doing, he kissed her thoroughly because he was putting all of his passion into it.

Finally, after what seemed like eons, Sheldon let her face go. She pulled back slightly, so she could smile down at him.

When he smiled back, Penny saw the reflection of the first falling meteor in his dazzling blue eyes.

Sheldon used to hate having people in his room.

It suprised him when he found that having Penny there made it more comfortable for him to sleep. Lying on his side, which he hadn't done since he was young child, and curling his long frame around hers, he felt like two puzzle pieces fitting together. In all the chaos and disorder in the universe, this was the one thing that felt right. He heard her breathing softly as she drifted to sleep, and he curled a blonde lock or hair around his index finger. His nose nuzzled gently against the back of her neck, taking in the scent of her perfume. She was wearing his Batman boxers and plain white tee-shirt, and part of her smelled like him.

Penny was his. Her scent mixed with his own confirmed that.

Shifting in her sleep, Penny rolled over so she was facing Sheldon and their stomachs were touching. His face was arching over hers on the pillow, and she curled close to his neck. He felt a current travel through his body when he felt her lips on his throat, accidentally embracing his skin like the touch of a dewy rose petal. He shivered delitedly. He didn't know that women could make men feel this way. Having not grown close enough to a woman to develop feelings for her in the past, Penny was Sheldon's first taste of real love. All his previous feelings for other human beings were washed away when he was with her, the same way everything else faded away in his mind when she walked into a room.

She was a part of him. It was humbling for Sheldon to realize that he had become part of such a timeless, irreversible thing like true love. He really hadn't even believed in love before. It was simply chemical reactions, after all.

But Sheldon couldn't blame all these feelings on chemicals. It was far more complicated than that.

It was love.

"Sheldon, please!" Penny's voice was shot and desperate as she watched him walk out the video store with his hands shaped in fists.

The tall man was following a blonde-haired, brown-eyed man out of the store. His name was Raphael, and he was one of Penny's ex-boyfriends. They had run into him in the store, and Penny had treated him civilly. Raphael had made a snide comment about how Penny was desperate and ugly. Of course, Penny burst into tears and Sheldon came over from the Horror section and been trying to talk with him.

Yelling after the retreating blonde man, Sheldon chased him out of the store. "What did you call Penny?"

"An ugly slut." He turned around and grinned, watching Sheldon pace towards him.

Sheldon's outrage was made clear by the way he glared and blinked slowly, talking at a slow pace like he did when he was talking to a less intelligent life-form. "Take it back, or I will make you regret you were ever conceived." He growled.

Raphael laughed. "Make me."

And with that, Sheldon's fist shot out and connected with Raphael's nose. He packed more power in his punch than most people would think, because he harbored lean muscles under his long-sleeved tee-shirts. Penny was standing in the doorway, partially mortified because she had caused the scene and partially proud that Sheldon actually hit Raphael. The blonde man fell to the ground cradling his nose and howling in pain.

Sheldon sniffed, looking at the sight with disdain. "She's the best woman any man could ask for."

Sheldon's mind was reeling as he watched Penny linger over him.

His vision seemed to spiral as she rested her head on his chest so she could listen to his heart beat. They were lounged out on the couch in the early morning light, and he watched as she floated in the dust particles spinning around him. She was like all of the symptoms a drug should have, but thousands of times stronger. His complex mind could only function on one thing whenever Penny was with him: her. He was trapped like a spider in his black widow's web, and didn't mind feeding her brilliance, if only to have his soul be a part of hers for the rest of eternity.

She made him feel like one of those dust particles, floating on the boundless plane of space and time, like he had no purpose and no intentions, but somehow he knew and he wanted and he felt.

He knew that he wanted her, and it made him feel so alive.

Penny always made Sheldon's chemicals react.

For instance, sometimes Sheldon didn't understand simple concepts when he was with Penny. Like breathing.

Of course such a captivating woman would steal a few heartbeats, he reasoned, it was all part of the chemicals. But making him forget to breathe? That part had to be psychological.

Leonard, Penny, Tracy, Raj, and Howard were swimming in the clear lake up at Mrs. Wolowitz's vacation house. Sheldon wasn't in the water, but did stay sitting on a chair on the dock. He watched his friends frolic in what had to be very germy water, and worried constantly about Penny and the possibility that she could get an infection or parasite or even radioactivity from such infested water.

He watched as her hands gripped the end of the dock, and she pulled herself up onto the wet wood. She half-crawled out of the water, tossing her head back so her hair flipped over her shoulders. She stood, and walked over to Sheldon with a small smile on her face. He took in her figure dressed in his swim shorts and tee-shirt, breath hitched in his throat, and felt a fire light itself inside of him. He mulled over the possibilities in his head, trying to remember what it was exacly that he was forgetting, but not reaching the answer because he was watching the way the muscles in her legs moved and how the fabric of his clothes clung to her as she walked.

When she got to him, the realization finally hit him. He took in a deep breath and let it out, closing his eyes to focus on getting oxygen to all of his cells. He felt her grasp his hand, tugging him out of the chair. "Come on, Sheldon." She taunted him. "Join us."

Her voice was all too enticing. Standing, he finally gave in. He watched her eyes light up and how her wet hair traveled through the air as she turned and ran to the end of the dock. He followed, and they leapt up into the air above the lake together, holding hands and letting smiles adorn their faces, before crashing down into the blue water below.

They way Penny made him feel, Sheldon would follow her anywhere.

Penny was being cradled in Sheldon's lap, watching the stars with him. This time they were on the grass alone, and Sheldon was ducking his head so he could quietly press his lips against her ear. She loved it when he payed so much attention to her like that; whether he was kissing her neck or her fingertips or her collarbone or her ear, he always made sure to do it thoroughly. Every time she felt his mouth on her skin, she felt as if she were being branded by him. She was his, and only his. It seemed so definite and irreversible.

Sheldon pulled his mouth away from her ear for a second. "Penny?" He addessed her quietly.

She giggled because his breath ticked her ear. "Yes, Sheldon?"

He hesitated a moment, hunching his back slightly so he was surrounding more of her. His breathing slowed, and she felt his tongue as he licked his lips in anticipation. "Will you marry me?" Those four words danced around her mind, making her dizzy and see stars in her vision where she definitely wasn't supposed to be seeing them. Sheldon continued to talk in her ear. "I mean, I know its custom for a man to ask a woman such a question when he feels like he has to live out the rest of his life with her, in order to fufull himself as a human being..."

Penny twisted her head around enough to her lips met his and silenced him. "Yes." She smiled against his lips as she pulled back to say her answer.

She could feel his wild heatbeat slow against his ribcage, and listened to his silence when he forgot how to breathe.