"What is it?" asked Martha, looking at the thing the Doctor held in his hand. It looked something like a teapot with a few too many protuberances and an unhealthy penchant for lime green paint, but the sonic screwdriver had identified it as the source of the interference that had been preventing the nearby human colony from communicating via anything more complicated than a semaphore tower. The inhabitants had been entirely cut off from the ships that hung in orbit around the odd little planet the Doctor and Martha had found themselves on after the TARDIS refused once again to take directions from her pilot, to devastating effect.
That and the fact that it had been humming in a vaguely upsetting manner since the Doctor had removed it from its little alcove in the cave wall (to which it was still attached by a number of thick tubes) made Martha reasonably sure that any resemblance it held to a kitchen appliance was only skin deep.
"I'm not sure," breathed the Doctor, putting on his glasses. He turned the possessed teapot this way and that, scrutinizing it.
"So in other words, you have no idea," smirked Martha, hands on hips. "Some savior of the galaxy you are. Can't even identify a space teapot."
"Teapot?" The Doctor looked blankly at her for a moment before looking back at the object in question. He stared at it for several long moments, before a grin spread slowly across his face. "It does look like a teapot, doesn't it? Mind you, it'd take a human to make the connection. Never did meet another species quite so fascinated with boiling dried vegetable matter and drinking the result. Still, though, I can't say I don't appreciate a nice cuppa myself every now and then. Works wonders for the synapses, and you never know when you'll find yourself in need of a quick jolt to the brain. One time—"
"Concentrate, Doctor," said Martha. "The people in that colony are depending on us to get them back in touch with their ships."
"Ah. Yes. Mustn't forget what we came here for." The Doctor glared at the thing, willing it to divulge its secrets. Sadly, it did not.
He shrugged, and licked it.
"Oh," he said, as Martha stared, her mouth moving but no sound coming out. "Nithilian organic plastic. You can tell by the hexachlorophene they put on the outside to keep bacteria from getting into it—"
"I'm sorry, but did you just lick that?" asked Martha incredulously, having finally regained the ability to speak.
The Doctor looked up from the alien artifact and into the disbelieving face of his companion, his eyes wide and innocent. "I suppose so," he replied, clearly not comprehending Martha's objection to his employment of the scientific method. "Why?"
"You don't know where that's been!" exclaimed Martha, trying not to lose her cool. The words 'I sound like my mum!' flitted through her head, and she clamped her mind down on them, willing herself not to follow that train of thought. The fact that the Doctor was still staring at her in wide-eyed incomprehension really wasn't helping, and it was times like these that she had to work rather hard to remind herself of his age.
"Yes I do," he replied, gesturing to the alcove where he had found the object in question. "It was in this handy little alcove."
"Yeah, but where'd it come from before that?" demanded Martha.
"The Nithilians?" tried the Doctor. "They're notoriously cleanly people…."
"But you didn't know it was them until you'd already gone and licked it!" objected Martha. "And besides that, you have no idea how much bacteria it could have picked up since they left it there—"
"—The hexachlorophene takes care of that—"
"—Which, again, you didn't know until you'd already licked it. Have you even thought about how unlikely it is that your body will have natural protection against alien bacteria? Honestly, I don't know how it is we haven't both contracted some sort of horrible alien disease and died by now, with all the places you take me."
"But at least I'm being careful about it. You, though—going off and licking things you find in caves! What are you, five?"
Martha finally noticed the grin that had been growing on the Doctor's face for the past few moments, and broke off her tirade just as he was threatening to commence chuckling at her. She glared at him.
"Martha Jones," he grinned. "Always thinking."
"As opposed to randomly licking things, yes," she replied, testily. "What's so funny, then?"
"Well, for starters, you're right about the alien bacteria," admitted the Doctor. "If we were ordinary travelers, we would definitely have caught something or other by now. But we're not ordinary travelers, are we?"
"Are you saying that there's some sort of Time Lord technology protecting us?"
"Yep." The Doctor popped the p on the end of the word purposefully, feigning a pensive look for a moment before going back to the grin. "Just one of the many benefits of TARDIS travel. Good thought, though."
"You still shouldn't lick things," said Martha, unwilling to drop the argument. "You could still end up ingesting something that disagrees with you."
"I'll keep it in mind," he conceded, though in a tone that suggested he would do nothing of the sort. Martha sighed.
"So what's that…Nithinian plastic thing, anyway? You said you'd seen one before."
"Nithilian organic plastic, and yes, I've come across one of these before now." The Doctor pointed the sonic screwdriver at the base of one of the tubes that ran between the object and the cave wall, the blue light flickering for a moment before the tube came away with a sickeningly wet crunch. Martha winced.
"What does it do?"
The Doctor moved on to the next tube, chuckling. "It blocks transmissions."
"Because the Nithilians think it's funny," explained the Doctor, detaching the last of the tubes. "Their idea of a practical joke is to throw an entire colony into chaos. They don't mean any particular harm by it, but I think it's safe to say that most other species don't appreciate their brand of humor."
"Ah. So that's it, then?"
"Yeah. Now that we've disabled the transmitter, the colony's communications should be up and running again. We'll just drop this off with the governor, and then we can be on our merry way."
He tucked the defunct transmitter under one arm and proffered the other to Martha, who took it.
"So that's the big crisis?" she asked. "A practical joke? What's next, are we going to save the Earth from whoopee cushions?"
"You never know," grinned the Doctor.
Martha rolled her eyes and slapped him on the shoulder, which served only to fuel his amusement. 'You never know,' indeed!
Deep down, though, she was not entirely sure that he was joking.