Disclaimer: I do not own Sherlock Holmes, John Watson or 221B Baker Street. Not in the slightest.

Summary: After Sherlock reads an article on the benefits of kissing, he convinces John to take place in a few snogging sessions. . . for science! Lots of medical lingo. There will be five parts in all.

Warnings: Some mild cursing.

Word Count (this part): 1,326

Pain Relief

The day after the pool experiment, John beat Sherlock to the punch.

John had just finished making tea and made his way into the sitting room to give Sherlock a cup. Sherlock sat crouched on his chair, his fingers steepled, and his eyes following every single move John made with utmost concentration.

John set the cuppa down on the table in front of Sherlock and sighed, looking down at his flatmate.

"I can tell by the look on your face that you are going to need me for an experiment again." John folded his arms across his chest. "Get on with it, then; what do you need me to do?"

Sherlock grinned up at him mischievously. "This one will be a bit more," he paused, "odd than our previous ones."

John shook his head in disbelief, wondering how it could possibly get any more odd than it had already been.

"Care to elaborate, then?"

Sherlock continued to stare at John as he said, "I am going to bite my lip to a point in which it breaks the skin slightly; enough for it to hurt and bleed a tiny bit." Sherlock tilted his head slightly and pointed his steepled fingers in John's direction before continuing.

"Researchers have found a natural chemical in saliva called opiorphin, which is six times more potent as a pain-reliever than morphine. I need to test how quickly the opiorphin stops the pain versus how long it takes for a low level of morphine to take effect."

John glared down at Sherlock as he said, "I'm not going to let an ex-addict take morphine, Sherlock."

"This experiment must be done!" Sherlock said irritably. "Using opiorphin as a replacement for morphine could reduce the risk of addiction in people who use pain-relievers." He paused for a moment, a sly grin replacing the irritated look from his face. "You want that, do you not? Being a doctor and all?"

John considered it for a moment.

'He's right, of course. Morphine is extremely addictive, and it's overall not good for you. . . . But there's no way in hell I'm letting Sherlock touch that stuff. Not since I know about his past.'

John was about to tell Sherlock no, strictly because he had no intention of allowing him to use the morphine afterward, but another thought wedged its way into his brain right as he was about to speak.

'What if I refuse to take place in the experiment? He could easily find someone else who would let him use the morphine. . . . and there's no way I'm letting that happen.'

With that thought, John made up his mind.

"I'll do it," John said. "But under one condition."

Sherlock quirked his head to the side in interest, his eyes slightly narrowed.

"And what might that be?"

John folded his arms across his chest as he stared right back at Sherlock.

"I receive the cut on my lip, and I take the morphine."

Sherlock's facial expression went from interested to confused. "Why?" He asked.

John shrugged. "You're an ex-addict," he said. "That makes you more likely to either relapse or find a new addiction in the pain-reliever. . . And I'm not going to let that happen."

Sherlock didn't have to be the world's only consulting detective to realize that John wasn't going to let him take the morphine. John had seen too much go wrong with his sister to even risk losing another person to addiction.

The detective stood up from his crouched position so he was standing with the back of his legs pressed against the chair.

"Fine," Sherlock said, clapping his hands together as he took a step toward his flatmate. "We'll have to wait a few days until I can get my hands on the morphine for the second half, anyway."

Sherlock suddenly reached out, gripped the front of John's jumper and pulled him close, causing the doctor's breath to hitch in surprise. A barely noticeable smirk played across Sherlock's lips, but John only had a fraction of a second to comprehend the undeniably smug appearance of it before his mind went completely blank.

Sherlock's soft lips met John's in a hungry, surprisingly aggressive kiss. The possessiveness that John could feel simply radiating off of Sherlock in that first moment nearly knocked him off his feet. The doctor realized that, while he may have never been one to take the submissive role, he was willing to let Sherlock do whatever the hell he damn well pleased if he continued to kiss him like that.

John felt himself being pushed backwards until the back of his legs met the resistance of the couch cushions. His lips briefly lost contact with Sherlock's as he fell back into a sitting position, but the detective quickly straddled John's lap and reattached their lips with the same aggressiveness that the last kiss had started with.

Sherlock placed his hands on either side of John's neck as he ran his tongue over the doctor's bottom lip, just as the latter had done to him at the pool the night before. As soon as John granted him access, he felt Sherlock quickly, softly nip his bottom lip; not hard enough to draw blood or even remotely hurt, but enough for John to feel it. After a few seconds, Sherlock bit the spot again; harder this time. John could taste blood, but, while the spot stung slightly, it was by no means unbearably painful.

Sherlock suddenly pulled back from the kiss.

"On a scale of one to ten, how badly does it hurt?" The detective asked, his voice a bit deeper than normal.

John's eyes opened just as slowly as his thoughts became coherent. "About a three," he replied, his eyes focusing for a short second on Sherlock's enlarged pupils.

"Perfect," was all Sherlock said before bringing his lips back to John's.

Sherlock moved one of his hands from John's neck to the back of his head as he licked the slightly raised sore spot on his bottom lip. John shivered, the pleasure of kissing mixing beautifully with the sting of the cut. The doctor wanted more, however, so he leaned up a bit and captured Sherlock back in a proper kiss. For a few blissful moments, they kissed like they had the night before.

But Sherlock once more ruined it by pulling back.

"Does it still hurt, John?" Sherlock asked slowly, slightly breathless from the last kiss.

John took a moment to concentrate on the spot on his lip. Amazingly, there was no longer any sort of pain there. The surprised look that flashed across John's face was enough of an answer for Sherlock.

The detective scrambled off John's lap and pulled his phone from his pocket.

John heard Sherlock mutter, "25 seconds for the opiorphin to take full effect," as he watched his flatmate typing away on his phone.

"Thank you, John," Sherlock said, never taking his eyes off the phone. "You have been a tremendous help. . . I'll be sure to let you know when the morphine arrives in a day or two. Your lip should be fully healed by then."

With that being said, Sherlock made his merry way toward his bedroom, leaving an incredibly confused doctor in his wake.