Sherlock offered the notebook with both hands like it was terribly valuable. Mrs. Hudson sat down and flipped open the cover to reveal a neat table in Sherlock's best handwriting.

"What's this, dear?"

Sherlock took the seat across from her and picked up the tea she'd insisted he at least taste. Possibly his only calories all day. "An experiment," he answered. "A small one, really. John insists it's impolite to make any significant amount of noise during sex - that it's rude to one's neighbors. His room has a smaller bed, though, and I categorically refuse to relegate all our amorous activities to upstairs. You're ideally placed to gauge the accuracy of John's concerns."

Mrs. Hudson put on her reading glasses to get a closer look.

"Data collection is simple," Sherlock continued. "Just note date, time and duration our sexual activities are audible. I'll vary my volume and we can discern the correct decibel level at which John and I won't be intrusive."

Mrs. Hudson closed the notebook, patted it, and handed it back with a gentle smile. "You tell that doctor of yours not to worry. I turn off my hearing aids and you two boys can enjoy yourselves as much as you like. Especially whatever it is he does that makes you say his name like that."

Sherlock actually blushed.