A/N: Hey guys and gals, I'm back for a bit and I felt like writing a little. I saw the first episode of season 3 and I like that the main plot is still based around the sibs. Don't worry I'll update Gravity sometime this week. I had this drabble stuck in my head and I just had to write it down. Enjoy some cliché Thundercest.

"You're hopeless."

They were in his bedroom -the lair- her standing by a stupid dry erase board, and him lying listlessly across from her on his bed, trying to learn how to fall into a deep sleep with his eyes open.

"Hey, it's not my fault." He runs a tired hand over his face. "Physics comes easier to me than this stuff. You don't need genetics to launch rockets."

He was just about to give up, and settle for, deep, deep sleep with his eyes closed, when he heard a frustrated sigh.

"You're a Junior in high school and yet, I'd be better off teaching a dog than you."

If that was a challenge then he was too drained to acknowledge it.

"Come on Phoebe, I'm trying over here." His head jerked up. "If you can't help me Mom and Dad will ground me for two weeks."

"So what." She responded, folding her arms.

"I won't be able to crash the school's Alumni ceremony on Friday." He said in a matter-of-fact tone.

"Which proves that I shouldn't be helping you anyway." She rolled her eyes.

He huffed and tossed an uncapped pen to the floor. One of his 'man-fits' as Phoebe often referred to them. Sure, they didn't usually see eye-to-eye, his annoying and her complaining but that worked for them.

He wrestled between the usual thrill of aggravating her, and that other prickly, irritating need to see her not upset, before sitting up on his mattress.

He glared at her.

Crossed his arms.

And grunted.

Then his eyes flickered softly between agitation and giving-in, and he sighed.

Phoebe took that as a sign that he was serious now. She cleared her throat and began. "A Punnett square determines the probable physical traits between two parent's offspring."

"Baby making huh, well that doesn't sound like something far off from my kind of expertise...if you know what I mean." He suggestively winked at her, biting back a smile.

"Gross." Phoebe stared at him for a long moment, eyes narrowed by how much of a pig her brother really was. "We're not talking about the poor girls who choose to get in bed with you, we're talking about the beauty of Biology."

For some strange reason, talking about Max's experiences with other girls bothered her. Like a hollow feeling pelted in her gut at the thought that he had been with other girls so casually and probably frequently.

"Fine, whatever." He mumbled all cool like and turned his attention to his textbook.

"Now, if two people have a child you can use a Punnett square to roughly guess what they're going to look like." Her shoulders were a bit straighter and she stood a little taller.

She couldn't help it. She just loved when she knew about something that Max didn't.

"You make it sound so simple, why don't I get it?" He pointed at the dry erase board. "Break it down for me, Pheebs."

Phoebe thought to herself for a moment, pacing back and forth in front of Max while he watched the wheels in her head turn. Even in an old pair of yoga pants and an over-sized t-shirt, he didn't mind the view. He liked when she wasn't overly done-up. She looked good.

"Okay...how about this." Phoebe blurted. "If Mom and Dad were to have another kid-"

Max immediately interrupts. "Don't even finish that sentence."

Without realizing where she was heading, she scrunches her nose at him. "Good idea." She shuddered. "How about this...um -if we were to have a kid,"

"Huh?" He questioned, although he was wincing for dramatic effect, the example didn't disturb him as much as he thought it was supposed to. He would wonder to himself about that later.

"Just listen." She said, lips quirked. "If we were to have kids, there'd be a better chance of them looking like me." Phoebe smiled confidently.

Max instantly took offense to that. "Why?"

"...It's really more about the genotypes, and how the alleles interact with each other. So..." She scribbled letters on the board, and Max tried to understand why Phoebe was drawing what looked to be a failed attempt at tic-tac-toe. "the alleles are different, so the offspring will be heterozygous."

His eyes glazed over -even though he was trying really, really hard to stay with her.

"In English please."

"Ah, okayyy." She tapped her finger on her chin for a moment. "How about this? Let's start simple."

He nodded. "I like simple."

She pointed to herself. "I have dark brown hair."

"Really?" He asked with spiked brows. "Because I thought you were a blond all my life...?"

Her eyebrows furrowed, which was always cute and he loved making her do it.

"Haha funny," she deadpanned. "But as I was saying...I have dark brown hair and you have light brown hair. So biology teaches us that certain traits are more common than others."

"But I thought brown was the more common trait."

"It is." She smiled prettily at him, eyelashes batting as he rolled his eyes. "But my dark hair is more common than your dusky brown hair."

"So then, why don't I have the same color hair as you?"

"Because you're weird." He could hear the playful tone in her voice from a mile away.

For once he's thankful that she gets him, willing to make light of what seems to be a boring -though he'd never mention it- but slightly interesting tutoring session. A much needed break is what he craves and this is his opening.

"Hey! Take that back." Max threatened, pretending that the jab Phoebe took to his ego actually bruised him.

When Phoebe shook her head and refused, he decided to force the words out of her. He quickly stood up and grabbed her by the waist, pulling her up and over his shoulder. She squealed in his arms, surprised by how effortlessly he hauled her up and then let out a small gasp when he not-so-gently threw her onto his bed.

This was much more interesting than some 'puny square'.

Not a second sooner, he's on top of her, wrestling, and his hands are tickling all over her, any part that she isn't trying to shield away from him.

"Max, stop!" She cried out in a fit of giggles.

"Say the magic words." He laughed with her, eyes hopeful and wide.

"Okay, okay...you're n-not weird...at all." She gasped out, trying to regain her composure while taking an obvious notice to the sudden shift in the room.

Max stopped but didn't respond, his hands just resting above her stomach and she felt every inch of her body buzzing with anticipation that was foreign to her. This didn't seem off, yet it was brand new territory to both of them.

He relented for a moment, not realizing how nice it felt to have her pressed against him or his hands on her body, but he eventually pulled back. Using his arms to now brace his weight over her. He could feel Phoebe's grip on his biceps tighten, or maybe it was his overactive imagination.

"The point is, as indescribably bizarre as it may seem," she hated that she sounded so breathless. "We share genetic traits but we're different. This is basically just another way of describing that, and explaining how it happened."

"...So, our kids would have your eye color because..." His voice was sharp, tight all of a sudden.

"Because," she paused for a moment and licked her lips. "I have dark brown eyes and you have..." She trailed for a moment, seemingly lost in his amber eyes. "You have lighter eyes." She could see the urge spiraling in his irises.

"Which means?"

"That makes my eye color dominant and yours is recessive."

"Hmm." He trailed off for a moment, considering the information. "That actually seems...almost interesting."

"Exactly." She smiled again, this time big and genuine. He couldn't stop his own lips from tilting in response. "See, biology isn't so boring and lame once you understand it a little better."

"Yeah," he said, huskier than intended. "I guess it's not so bad..." He was silent for a long moment, his eyes darting back and forth before finally resting on her mouth.

"It's not." Phoebe whispered, hesitantly leaning closer to him.

They held still for a second, a second full of worry that they shouldn't be doing this, their minds telling them both to back away and get back to studying. But Max shook those thoughts right out of his head before tugging her closer and slanting his mouth over hers carefully.

His lips pressed against her mouth and she felt a jolt rush through her body. Her chest was so full that she felt as though she might burst. Max began to move his lips slowly, almost experimentally, giving her all the leeway if she wanted to pull away and stop this.

But Phoebe followed his lead, sliding her mouth in time with his own. She felt his tongue trace her lips hesitantly and before her mind could process what was happening, she opened her mouth in response and pressed her body closer to him. He made a low noise in the back of his throat that sent a shiver through her entire being.

They continued to explore each other, the push and pull of her taste pushing morals to the wayside. Max's hands felt so firm against her hips and rips, fingers running up and down her torso steadily dancing with the fire burning beneath her skin. She took a shallow breath through her nose, inhaling and feeling every part of him surround her in the most amazing way.

When they finally pulled apart he hovered close, Phoebe didn't mind at all. In fact, she might have needed his presence more than anything at this moment. Her mind is going one hundred miles a minute and she uses his solid frame to steady herself.

"...Wow" She uttered in a daze.

"Yeah..." He breathed, battling with himself on whether he should bring his lips down on hers again. But he doesn't want to press his luck, they'll have a lot to talk about once they come back to their senses.

He shifts, slowly getting off of her and offering a hand to help her up. She takes it wordlessly as she quietly gathers her things.

When he finally hands her, her biology book, Phoebe mumbles a quick 'thanks' and blushes tremendously.

"Maybe later, you can um...help me with Trig?" She proposes for reasons unknown to him, but very known to her.

She doesn't know why she's doing this.

"But...you're great at math." His eyes squinted slightly and his vision felt out of focus.

Silence.

"I know."