“Doctor,” she demanded.  “What is that?”

The Doctor pulled himself out from under the TARDIS’ console where he had been tinkering without much success.  Some of the lights had been flashing on and off for no apparent reason, and he wanted to be sure there wasn’t a malfunction anywhere.

“What?” he said.  “Where?”

“There!”  Donna pointed at the snake-like creature, which was heading straight for the space the Doctor had recently vacated.

“Oh no you don’t!” the Doctor said, as he bent down and picked up the creature by one end.  The other end would itself round his arm.  The Doctor stroked it absent-mindedly.

“Are you sure it’s safe?” Donna asked.

“Oh yes,” the Doctor said happily.  “This is a snock.”

Donna was about to ask what a snock was, when she spotted a similar creature, although dull grey in colour, also making its way across the TARDIS floor.

“Quick, grab it!” the Doctor yelled.

Rather reluctantly Donna did so.  The second snock didn’t offer any resistance, but hung from her fingers, swinging slightly.

“That probably explains what’s wrong the console too,” the Doctor said.  “There must be a snock convention going on.  Which is fine, but I don’t want them in there.  See if you can find somewhere else for them to meet.  A laundry basket, or something.”

“A laundry basket?”

“Yes, you know, plastic thing for carrying washing in.”

“I know what a laundry basket is, spaceman, but do you really have one in the TARDIS?”

“There’s bound to be one somewhere.”

Donna opened the cupboard which she had privately labelled as ‘White Elephant’.  Sure enough shoved on top of a pile of inter-galactic tat was a laundry basket.  She got it out and carefully dropped the snock into it.  The snock promptly curled up.

The Doctor placed his own snock in the basket, where it raised itself into a vertical position before forming a spiral and then sinking down again, next to the first snock.  Almost immediately five more snocks emerged from under the console and slid across the floor, before swarming into the laundry basket.

The Doctor looked at the console and said, “The lights are all working correctly now.  I was right, it was a snock convention.”

“What do we do with them now?” Donna asked.

“We get them to a suitable planet as soon as possible, because we really don’t want them breeding on the TARDIS.”

“Can they breed?  None of them look anything like any of the others.”

“That’s the point.  You only ever see odd snocks, never a pair.  It doesn’t stop them multiplying though.”

Donna looked as if she was going to ask another question, but then thought better of it.  Some parts of the universe were always going to remain a mystery to her.