"Are you quite done?"
Donna paused for a moment and fought for breath, before succumbing to another fit of laughter.
"That's a no then", the Doctor sighed.
Donna leaned against the console, pressing her arms against her midsection and let out another stream of snorting laughs.
"I'll have you know, regeneration is very serious business," the Doctor said, crossing his arms and giving her a very stern look.
"You," Donna panted. "You regenerated..."
"Yes, and it is no laughing matter."
"You regenerated into a TEN year old!"
"I'm not ten!" the Doctor cried. "I look nothing like ten!" He straightened his back and smoothed his hands over his shirt, that didn't really fit very well any more. "I look good. You're just jealous."
"No, sorry, you're right," Donna said and sobered up a bit. "To be fair you do actually look more like... eight." And then she was roaring with laughter again.
The Doctor sighed and gestured wildly in a manner he suspected was very un-Time Lord like. He'd have to do something about that. "I am over 900 years old. There's nothing wrong with looking good for your age."
Donna looked like she was about to fall over laughing. Again. "If you die again, will you regenerate into a baby? Will I have to change your nappies?"
"I will not regenerate into a baby," the Doctor said firmly. Well, probably not; stranger things had happened.
"Is that how it works, you get younger every time you regenerate? Were you born really old - oh, were you grown in a vat? Stepped out all full-grown and now you're ageing backwards?"
The Doctor wasn't entirely sure this was the right time for a lesson on Gallifreyan procreation, so he focused on her first question instead. "Well, that's very, uh... complicated. It's a complicated process, lots of things can go wrong - you're lucky it didn't end up like the last time. Had to sleep for days. In the middle of an alien invasion."
Donna giggled. "Aw, is it your bed time? Do you want me to read you a story? You just go on and brush your teeth and wash your ears and I'll be right there. And the hair..." The Doctor tried not to flinch. "You are planning on having a hair cut before we go out in public, aren't you?"
"Donna. I just DIED. A little respect, please."
Donna smiled at that, a bit like someone might smile at a puppy doing something particularly adorable. It was probably going to be the best he got at this time. "Donna," he said casually. "When we tell people about what happened today, we don't have to tell them ALL the details, do we?"
"Oh, you mean the details of how you tripped over your own two feet and cracked your head on the pavement?"
"It was a brick, Donna! Not my feet, and I'm sure it was put there by someone very... sinister, what are you doing?"
"I'm calling Martha. She is going to LOVE this."
The Doctor furrowed his brow. The regeneration had gone unusually smooth - no memory loss or temporary insanity or coinciding alien invasions, and he'd got over the disappointing lack of ginger-ness quite quickly. But as he watched Donna dialling the phone in between giggles, he started to suspect that the problems had only just begun...