John Watson froze abruptly as Sherlock pulled the mug from his hand. He stood motionless for a moment, turned to leave, but then thought better of it.

"Did you –" he frowned, staring keenly at his stinging index finger, "did you just prick me when I handed you your tea?"

"Hmm? Sorry?" Sherlock, lying languidly on the sofa, had cradled the mug to his chest and was tapping his pale fingers on it idly.

John squeezed the pad of his finger with his other hand, and sure enough, a little crimson pearl of blood welled up from a near-invisible puncture in the ridges. He dropped his shoulders and rolled his head back, defeated, but still irritated. "My finger, Sherlock, you pricked it with a needle, just now. You took blood."

"Oh, yes. Strictly necessary. You don't mind, do you?" He produced, from the bottom of the mug, a small strip of white paper, punctuated by a neat red splotch, which he held between the knuckles of his first and middle fingers for John to see.

He set his feet apart and crossed his arms over his chest. "Yes, in fact, I do mind. You can't just go taking peoples'…bodily fluids."

Sherlock cocked his head slightly to look up at John with one eyebrow raised.

"Yeah, alright, I'll take that, then." He reached down for the paper strip, but Sherlock was too fast for him, tucking it into the pocket of his dressing gown.

"Do you notice when you do that?" Sherlock demanded abruptly, craning his head back against the patterned pillow to look more directly at John's face.

"What?" He furrowed his brow, not quite done with the blood stealing business and not eager for Sherlock to change the subject.

He didn't answer, what he did, slowly, was slide his flattened tongue from his mouth, just a centimeter or so, pressed it gently against his lips, then withdrew it, leaving his mouth slightly open as he held John's gaze.

John was silent for a moment. Something about the directness of Sherlock's eye contact and the unapologetic parting of his lips was making him very uncomfortable. Now utterly confused, all he could do was throw out his hands in exasperation and wait for an explanation. An explanation which, as the seconds ticked by, Sherlock did not offer. "I –" he rolled his eyes, trying to stifle a sigh, "what are you on about? In, you know, words, if you don't mind."

"When you're uncomfortable, or anxious," He finally said, then did it again, painfully slowly, demonstrating the subtle tongue movement, apparently for John's benefit. "You do it rather often. You did it when you hesitated just then."

Yes, after the words "bodily fluids," he vaguely remembered licking his lips. To his chagrin, he had to consciously stop himself from doing it now, as he stared blankly back at Sherlock's intense, childlike scrutiny.

"You don't notice that, either, do you?"

"What?" He all but shouted, ready to be done with this conversation, slightly fed up with this odd little game of charades. True to form, Sherlock did not answer, only held John's gaze intently and pursed his lips slightly, in a bizarrely perfect imitation of John's other favorite facial expression. "That's not the same though, you do that when you're irritated, or when you want to say something, but you're stopping yourself." Casual and calculating as ever, Sherlock took a sip of his tea and turned his eyes back to the wallpaper.

"Well…" again, he had to stop himself from licking his lips. How strange that they felt so dry so suddenly. "This has been a highly informative load of fun, but I'll have my blood back now, please." He thrust his hand into Sherlock's face, tapping his fingers together in irritation. For a moment, Sherlock did not stir. He held his tea and inspected John's fingertips, the tiny spot of blood still belled slightly from the skin. Growing frustrated, John wiggled his fingers expectantly again, knowing that Sherlock was fully aware of what he should be doing, but was holding out for time, hoping that John would just get angry enough to drop the matter. He had already decided that that wasn't going to happen. He was making a point, and he would be damned if Sherlock's stubbornness won out.

He was shocked to a profound immobility when, instead of handing over the paper strip, Sherlock took hold of his wrist, not painfully, but firmly, pressing his thumb into the soft underside of his arm, and drew John's bleeding finger slowly to his lips. His smooth, wide tongue flicked from his barely-open mouth and dragged, warm and wet, over the small space between the first knuckle and the fingertip; it quivered with exertion, pressing firmly, taking its sweet time to cover the tiny distance. In a single, fluid stroke it swept away the tiny droplet, then lingered for a few long, pounding heartbeats at the very apex of John's finger, inundating his skin with the heat of Sherlock's mouth, saturated from both the press of his tongue and his soft breath.

Sherlock released John's wrist, broke contact, and sat up, glancing around vacantly. With a quick, casual step he was up off the sofa, stomping over the table and headed for the kitchen.

John stood, frozen. Blood pounded in his ears and he could feel the warmth of it in his face. His heart thudded in his chest as though it was trying to escape his ribcage and his hand trembled, still held out dumbly in front of him. He stared at it for a long moment, saw a slight glisten in the lamplight. With a strange mixture of curiosity and trepidation, he slowly brought his thumb up to gingerly touch his forefinger. It was damp.

He stood up straight, finally, and swallowed the dryness in his throat. He wiped his assailed finger on his jeans, rubbing away the last trace of saliva, and took a step back from the sofa. His breath was quicker than it should have been. He cleared his throat.

"Going out for a bit," he announced. To his immense relief, his voice sounded pretty steady. He hurried to snatch his jacket from the hallway before scuttling down the stairs.

Sherlock heard the door slam behind him and grinned coyly to himself. He slid his hand into his pocket and retrieved the bloodied strip of paper, turning it briefly over his fingers before dropping it into a sterile dish.

"If I could count how many times you licked your lips tonight, John Watson," He mused aloud, "I feel I would know a great deal more about you."