A/N: Why must the most persistent story ideas strike when I have a billion and one things to do? I finished this just before I posted it, and all the science is from Wikipedia, so any and all feedback is welcome.
Also, it is complete and utter crack. I'm sorry. I'm so sorry.
Feedback: Is love. Please review!
The Doctor smiled under the console as Rose's echoing steps came closer to the large room. He hadn't seen much of his companion lately. After their visit to 2012 a week ago, Rose had spent most of her free time in the library, pouring over old leather-bound tomes and writing notes on scattered sheets of paper. He'd tried to figure out what she was doing, but any time he got close she'd cover up her work and sweetly say that she'd tell him all about it when she was finished. So he'd left her to her work. Good for her, finding a topic she was so interested in. Study and learning were good for the mind—kept you sharp. And that was definitely what they needed, all the running for their lives that they did.
He pushed himself out from under the console and looked toward Rose, about to speak, when her attire caught his eye. Instead of her usual hoodie and jeans, Rose was wearing khaki trousers and a blouse, her hair pulled back in a smooth bun at the nape of her neck. She looked…academic, as if she'd just come from a university campus. It suited her, in a way, an outward representation of all the intelligence he knew she had.
She spoke as he stood and brushed bits of wire off his trousers. "Doctor, I've been thinking—"
"Wonderful thing, thinking," he interrupted, smiling widely at her. "All that studying and thinking and pondering you humans do. It's what's kept you prospering while other races have failed."
She smiled indulgently at his ramble and continued on with her thought. "I've been thinking about the Olympics, and Chloe and her mum. Do you remember when I figured out that Chloe was connected to the scribble monster?"
He smile got even wider, if that was possible. "Of course I do! That was brilliant, Rose, how you deduced that. I was so proud of you. I—"
"You looked like you wanted to snog me up against the console."
His smile faltered. "I did?"
Her tongue poked out thoughtfully as she leaned against the railing. "Yep. Of course, you're always sending me looks when you think I don't notice."
Bollocks. He thought he'd been more subtle than that.
She continued. "But this one seemed different, somehow. More…intense. I had an idea, so I thought I'd go to the library, do some research."
Was it getting warmer in the TARDIS, or was it just him? "Really?"
"Mm-hmm. And after a bit of searching, I found some amazing books on Time Lord anatomy."
"You…what? Really?" He'd forgotten he even had those. "You shouldn't have been able to read them."
"I couldn't, at first. But I asked the TARDIS nicely, and suddenly they were in English."
The Doctor grinned. "That's wonderful, Rose. She wouldn't do that for just anyone. But why didn't you just ask me? I could have told you anything you wanted to know."
Rose shook her head. "No, I needed to do this myself. And I'm glad I did, because I found the most interesting things." She moved, trailing her hand along the railing, the Doctor's eyes following her every move. "Like the fact that, superior species and all, a Time Lord brain looks a lot like a human brain. They're both structured the same—forebrain, midbrain, hindbrain. Though Time Lords do have a larger hippocampus—you would need more long term memory, as long as you live—and a much more developed cerebral cortex." She looked at him. "But you know what one of the biggest differences is?"
He was enthralled with her, blood beginning to pump faster in his veins. "What?"
"In humans, arousal, sexual and otherwise, is controlled by the reticular activating system in the brainstem, right between the midbrain and the medulla oblongata." The scientific names rolled off her tongue like honey, and he fought back a shudder. "Those parts of the brain control the body's autonomic functions, like breathing, digestion, heart rate. It's instinctual." Somehow, she made the simple word sound dirty.
"But Time Lords don't need a biological urge to procreate, do they? So the part of their brains that controls sexual arousal is located closer to the frontal lobe, which plays a part in, oh, so many things—abstract thought, problem solving, language, memory…stimulate one, and it's quite possible to stimulate another. Intelligence and arousal, so closely related. It's like an aphrodisiac, almost."
He was moving closer to her without realizing it, every beautiful word out of her mouth reeling him in until he was standing right in front of her, staring into her eyes and breathing heavily.
"So I have a good theory why the look in 2012 was so different. All that logic and thought and deductive reasoning—it was turning you on."
Before the Doctor had a chance to reply, she reached out and cupped him through his trousers.
His knees buckled.
"Oh, look," Rose said airily. "My hypothesis was correct."
"Oh," he managed, "that. That's not…that's not fair." He tried in vain to regain his equilibrium as she traced the length of him through thin layers of fabric. The voice in his head that said this was a Very Bad Idea was quickly quieting.
"No. You're…you're using my biology against me."
She giggled. Giggled. "Really? Cause I thought I was seducing you." She leaned closer to whisper in his ear. "Seduce: a verb, meaning to lead away from appropriate conduct; to induce to engage in sex; to win over or attract. From the Middle English seduisen, all the way back to the Latin subdūcere, meaning to withdraw."
"And that's only the beginning. I've been doing a lot of studying. I could go on talking for hours."
Oh, sod it all, he thought.
"Well," he murmured, huskily, "I think it would be best if we continued this in another location. Like a bedroom."
She grinned up at him. "And I think that is a wonderful idea."
Sadly, there was no more thinking for the next few hours.