Sherlock smiled to himself from his armchair as John walked through the kitchen to the back of the flat, his towel slung over one shoulder. It would only be a matter of time now. Sherlock was going to settle in for a quiet evening reading while his flatmate prepared for a night out on the town with Mike Stamford.
It wasn't long before a loud, unintelligible exclamation echoed off the bathroom tiles. An angry ex-army doctor stormed out of the bathroom wrapped in his dressing gown, holding a tube of 'toothpaste.'
"Whah-diddiss?" he demanded of Sherlock.
Sherlock glanced up briefly then returned his attention to his book.
"Toothpaste," he replied disinterestedly.
"Mar-mow-mimmum!"
Sherlock couldn't help it. A tiny smile played on one corner of his mouth.
"I'm sorry, John. I can't understand you."
"Mar-mow," John repeated slowly, indicating his mouth with an angry finger, "ee mum!"
"Your mouth is numb," Sherlock repeated blandly. "As if someone had emptied the toothpaste tube and refilled it with an anaesthetic as an April Fool's Day prank."
John's eyes widened in disbelief.
"Whar?"
"I know. It's only the 31st of March, but you'd be expecting a prank tomorrow and it wouldn't have the element of surprise. That would be so boring."