Originally posted on The Big Blue Box of Randomness. Since it's a full(ish) story, I thought I'd import it.

Happy Series 9 Day!

Clara Oswald was a very happy woman at this point in time, which really isn't saying much, since she currently was in the TARDIS. It doesn't really matter, either way. Let's just say she was very happy.

The reason? She had just figured out a secret that the Time Lords had been trying to keep quiet for centuries. And she wanted the whole world to know. Not the secret, but the fact that she had found it out.

"Doctor!" she yelled into the endless hallways.

"Yes?!" came the reply.

"I need you!" she yelled again.

"Why!" he called back.

"Come here!"

"I am!"

Clara turned around. The Doctor, in all his bowtie glory, was standing right next to her.

"What do you need me for!" he yelled at her.

"We can stop yelling now!" she yelled.

"But I was having such a lovely time...!" he whispered.

"You don't need to whisper either," she added.

"Okay."

"Right. I have figured out the secret of why Time Lords live so long."

"You already knew." The Doctor looked puzzled. "Superior biology, remember?"

"No."

"No?"

"No."

"No. So, I'll bite, why do we live so long?"

Clara looked exceedingly pleased with herself. "Pink elephants."

"Excuse me?"

"You heard me. Pink elephants."

"What do pink elephants have to do with long lives?"

"A lot."

The Doctor frowned at her cryptic answers. "What are you talking about?"

"You already know."

"Pretend I don't."

"Fine, then. Have you ever heard of, 'don't think of pink elephants?'"

"Yes..." he responded carefully. He could see where this was heading.

"So, the secret to immortality is to not think of pink elephants, right?"

"Right, and it's supposed to be impossible, of course."

"Ah, but that's where you're wrong."

"I'm wrong?"

"Yes, you are. Because Time Lords have superior mental powers, they can suppress the thought of pink elephants, and therefore be immortal."

"But Time Lords aren't immortal! We do die after a specific number of regenerations!"

"That's because, in some part of your mind, you actually ARE thinking of pink elephants. And that's why Time Lords have longer lives than most species." Clara leaned back, apparently proud of her logical explanation.

"I...see..." The Doctor was still trying to remember to breathe. That girl was just...impossible. "Well, you're absolutely wrong. That isn't why Time Lords live so long."

"Oh." Clara looked disappointed. "I was so sure... I guess I'll go look in the TARDIS library again."

She wandered off into the endless corridors again, presumably looking for the library. And possibly the swimming pool as well.

"She'll never figure it out," the Doctor told the TARDIS, patting the console. The ship hummed in response. "After all, who would even think about purple elephants in the first place?"