Sherlock knit his brows and looked up at the sound. It hadn't been loud, but it had been unexpected in the still quiet of a January afternoon at 221B. Across the room, John continued to read in his chair, apparently unaware of the small disturbance.
"Did you hear that?" Sherlock asked.
"Hmm? Hear what?" John said, glancing up.
"That little sound just now."
"No," John said shortly, returning to his book. Mystified, Sherlock returned to his laptop.
A minute later, the sound came again, a sharp but gentle pop. Narrowing his eyes, Sherlock looked suspiciously at John.
"You did that," he accused. "Whatever you did."
"Did what?" John said, eyes innocently wide. From somewhere near his opposite hip, the popping sound came again.
Sherlock rose and stalked over. "What is that maddening sound?" he demanded. "It sounds familiar, but I can't place it."
"Meditation aid," John said.
"What?"
"Or, if you like, stressbusting tool."
"You're not making sense, John."
"Or a cheesy costume for a classic but low-budget British science fiction show."
"John."
"Or, in its most pedestrian application, lightweight packaging," John said cheerfully, handing him a small square of it. "Quite addictive, actually."
"What do I do with this?" Sherlock asked, examining it curiously.
"This," John said, demonstrating. "Today is January 28 - the official day for appreciating bubblewrap."