"Good evening, Doctor Song," he said, nodding to her through the bars of her cell.
"Good evening," she replied without looking up from her book.
She was still sitting there, curled on her bed reading, the next time the guard came round. "Good evening, Doctor Song."
"Good evening."
Then, as he'd passed her and could start to see round the bend in the corridor... Hanging from every pipe, every alarm box, every light fixture... For as far as his eye could see...
Strips of thin white paper.
Everywhere.
He'd never seen anything like it before in his life; it had certainly not been there a few minutes earlier.
Turning around, he found Doctor Song standing at the bars of her cell, smiling brilliantly at him. "Happy Halloween."
For once, though, he managed to get the last laugh. He made her clean it up. And – this time – it took her all night long.