Sherlock manages to maintain his silence for several weeks before the curiosity becomes unbearable. He waits for John to arrive home from work, then calls his name.
"What is it?" John asks, still putting his coat up.
"In the interests of science," Sherlock begins, having already rehearsed his arguments and his counter-arguments to John's counter-arguments in his mind. "I would like to study your unique physiology. Just to satisfy my own scientific curiosity," he hastens to add. "No one else would know about my conclusions."
Sherlock isn't sure how to respond for a moment. Why wouldn't he? Because it's interesting, because it's different, because it's John. "You can do things no one else can. You violate the laws of physics, and I want to know how. This would be purely exploratory research, of course."
John looks at him consideringly and Sherlock's struck again by how very ordinary he seems. Shorter than average, with plain, dishwater hair and pleasant but unassuming features. He doesn't look like the sort of man who would be affiliated with the paranormal.
"I'll do it if you clean off the table," John says finally.
Sherlock hastens to clear the mess of experiments and notes from the dining room table. It means he loses two of his experiments, neither of which could be safely moved. Under normal circumstances, this would irritate him, but John's offering himself as an experiment instead and John's infinitely more fascinating. He gets everything put away and even manages to wipe the surface of the table down with a cloth by the time John finishes eating dinner on the sofa.
John fetches his medical kit from the shelf and hands it to Sherlock. Then, he hops onto the table and pulls his shirt over his head, revealing skin perfectly smooth aside from the raised scar tissue on shoulder and a normal amount of chest hair. He's physically fit, Sherlock observes with no surprise. Not as much as he had been in Afghanistan, but still moderately so from the running and fighting he's been doing with Sherlock on their cases together.
"Just the basics," John says warningly. "You're not allowed to do anything I haven't done before. And no fire."
"Of course," Sherlock agrees, and grabs one of his notebooks. "Heart rate and blood pressure first," he declares. "To establish your baseline."
John complies obediently as Sherlock records his vitals. All are well within the average range for a man of his age, fitness, and physical activity levels. He is feeling John's lymph nodes (Sherlock's not sure what they're supposed to feel like, but they don't seem much different from his own) when John asks, sounding confused, "Are you giving me a physical?"
"Is there any reason I shouldn't?"
"S'pose not." John's skin is warm and slightly rough under Sherlock's fingertips. He can feel John's jaw move as he speaks.
"Hold your breath," Sherlock says, pressing the stethoscope to John's chest. The dull roar of John's lungs goes silent. Then, it stays silent. Sherlock counts to thirty and John still doesn't inhale. "Are you in any discomfort?"
John shakes his head, so Sherlock goes back to counting. He gets to 130 before John inhales shallowly, only to say, "I don't need to breathe. Nothing's going to happen if you keep waiting."
He exhibits no signs of hypoxia. His pulse is strong. Sherlock frowns. "How can you not need to breathe? Your body needs oxygen to function. By completely halting your oxygen intake, your body should no longer be producing adenosine --"
John interrupts him with a roll of his eyes. "I already said I don't know how it works, just that it does. There's no point trying to understand it. I'm a doctor, and I don't understand it. Did you get all your baseline measurements yet? I want to sleep before it's the middle of the night."
"But there's hours left," Sherlock protests. Hours, where he could listen to John's heart and touch his skin and examine his body. Hours, and John wants to stop already?
Except, not. John's meaning is made clear when he lies down; his legs dangle over the edge, but the position puts his torso and head fully on the surface of the table. "It'll takes ages to close everything up when you're done," he says. "Trust me, you want to start now. Scalpels are -- oh, damn, I'd taken them out because Wednesday was playing with them. They're on the top of the fridge."
"You want me to cut you?" Sherlock's voice goes embarrassingly high and alarmed near the end of his question. He disguises his embarrassment with a cough when John looks at him.
"It won't hurt me," John says calmly. "Go on, I don't mind. Trust me, looking at a live body's a lot more interesting than a dead one."
This is true. Sherlock knows it's wrong, but there've been many times where he'd felt the urge to cut open a living, breathing body simply to get a better look. He never has of course, because Mycroft would know and tell their mother, and also murder is wrong. But he's wanted to, and to look at John -- to really see him, to peel him open and get a good look at what makes him John. Well. The thought makes his chest tighten with anticipation. "I thought you said just the basics."
John props himself up on his elbows to look at Sherlock blankly. "This is just the basics. No fire or feeding me to animals or sealing things in my body. But if you just want to look, you're welcome to look," John says, as if Sherlock carving him open to satisfy his curiosity is something more okay than Sherlock leaving an uncovered head in the fridge.
"With a knife."
"...Yes?" John's brows furrow. "You'll need a saw if you want to remove any bones. I haven't got one in my kit, so that'll have to wait for later."
Ah, Sherlock thinks. This must be how people feel when they speak to him and he says something a bit out of the ordinary.
"Is that a problem? If it's important, you could probably use a hammer, but putting all the pieces back together afterwards is a bit harder." John looks down and pokes his chest. "Ribs would be fairly easy, I imagine."
"No," Sherlock says. "It's fine. This is fine."
When Sherlock returns from fetching the scalpels from the kitchen, John has positioned himself on the table like a body awaiting autopsy. He's perfectly still, save for the gentle rise and fall of his chest as he breathes. Sherlock touches his chest. John stops breathing. His eyes are open and Sherlock can see him blink. The skin beneath his palm is warm, and when Sherlock presses harder, he can feel the steady thump-thump of John's heartbeat.
But. But John's not breathing, and as the seconds tick by, uneasiness builds in Sherlock's chest -- John's not breathing. He pulls his hand away. "You should -- you should breathe," Sherlock says, feeling embarrassed and a little bit stupid. John doesn't need to breathe (but what if he does?).
John inhales obediently. "Sorry, thought it was distracting you," he says.
It does, but not in the way John thinks.
Carefully, Sherlock selects a scalpel. The handle is thin and round, blade perfectly clean. It has several minute scratches on it. "This one?"
"It doesn't really matter, but I would have picked the number four handle -- the flat one there, yes," John says as Sherlock picks it up; its blade is much larger, of the sort Sherlock's seen used in autopsies.
Sherlock hovers the blade over the hollow of John's throat, ready to press down. John is perfectly trusting beneath him, and Sherlock thinks, It's all right. It won't hurt him. He can cut into John's skin. He's about to, he's going to. John will let him.
"Wait, stop," John says abruptly. He sits up, and Sherlock can't tell if what he's feeling is relief or something else. "I can't see from there. I need to..." John disappears into the kitchen and returns, several moments later, with a plate and a meat cleaver.
Sherlock takes the cleaver when John offers it to him; the plate goes on the table, on top of a stack of texts John pulls from the bookshelf. John lies down again. Sherlock frowns. "What's this for?"
"I can't see if I'm lying down. Cut my head off first and put it on the plate so I can have a better view."
John directs Sherlock as he positions the blade ("Lower, keep as much neck as possible or I won't be able to turn my head"), but when it comes time to actually make the cut, Sherlock hesitates. What if he's wrong? What if he hurts him? He touches the sharp end of the blade to John's throat.
He could push down right now and his strength would be enough to sever John's head from his shoulders. It's all right, he repeats to himself. He wants you to.
"What's the matter?" John asks when Sherlock hasn't moved for several seconds. He wears a small, puzzled frown. "Is something wrong?"
I don't think I can hurt you, Sherlock thinks helplessly. He's never been in this sort of position before, and while his mind still remembers the sight of John's hand moving independently from his arm, that doesn't mean it'll work again.
John's still waiting for an answer.
"I can't," Sherlock says.
"Why not?" John asks. He seems somehow perplexed at the idea that Sherlock might be uncomfortable decapitating him with a meat cleaver. He figures it out when Sherlock can't find the words to express his thoughts. "Oh," he says. "Oh. Would -- would it be better if I did it? The head part, at least."
Sherlock nods, feeling foolish. Stupid. Stupid. He trusts John, trusts that if John says he won't be harmed by having his head removed, then he won't. But there's a niggling doubt in the back of his mind that asks, but what if?
He doesn't cringe when John takes the cleaver from his hand, but it's a near thing, and he does wince, squeezing his eyes shut, when John swings the blade up and then back down with a flick of his wrist. It makes a sick, meaty sound when it hits the flesh but no blood sprays onto him, and before he's managed to fully process the noise (struck the flesh, went in, didn't hit the table), he hear's John's voice, saying mildly, "Fuck."
When he opens his eyes, he sees that John hasn't quite managed to sever his head -- the blade has a good two inches to go, and hasn't even cut through his spinal cord. There's no blood, giving the whole scene an unrealistic quality, as if he's looking at a particularly skilled magic trick. John raises his hand and wiggles his fingers briefly at him.
"Hmm," Sherlock says, because it's clear that while any normal human would have been bleeding to death by now, John feels fine. A little annoyed, if the expression on his face is anything to go by as he awkwardly tries to push the blade further down without the proper leverage, but physically fine. "Do you need help?"
John nods, a short rise and fall of his chin. "I've never tried to do it like this before," he explains. "When I was a kid, Harry always did it for me. Just push down on it. Use your weight."
Sherlock does so; there is first the crunching sound of him cutting through through John's spine, then the solid thunk of the edge of the blade hitting the surface of the table. The sound makes something inside him cringe, but he relaxes when it's over and he looks at John's smiling face.
"That wasn't so bad, right?" John asks, turning his head from left to right. When Sherlock removes the cleaver (there only a small smear of blood on it, not even enough to form droplets), he can see John's trachea, clear and open as he speaks.
And all right, that's really fascinating. He can see John's carotid arteries and jugular veins, wide open and full of blood that doesn't spill out. "What's your blood pressure?" he asks, because there must be blood pressure, stronger than the ambient pressure. He's seen men with their arteries cut, and it's always resulted in a strong spray of blood. John has to have blood pressure, or he wouldn't have proper circulation.
John shrugs. "Same as it was ten minutes ago, I'd expect. Can you put my head on the plate now? I can't manage it myself. I'm always uncoordinated for a few minutes after it happens."
Lifting John's head doesn't feel anything like lifting a severed head normally does. Normally they're cold and it's slightly distasteful. This doesn't feel like that. This feels like he's imagined cupping John's face would feel. John's skin is warm with life, the skin rough with stubble and the flesh yielding against his hands. His pulse is strong under Sherlock's fingertips.
John licks his lips when Sherlock raises his head to eye level, and quirks a smile. If not for the weight of John's head in his hands, Sherlock could have just been touching him, for the sake of touching.
"I can't normally look you in the eye," John comments, when Sherlock sets him carefully down on the plate. "It's different."
"There is no physical connection between your lungs and your mouth," Sherlock says. John shouldn't be able to speak. That's not how speaking works. He touches his fingertip to the inside of John's trachea. "Can you feel this?"
John makes a strange face. "Yeah. It feels weird." When he speaks, Sherlock can feel a slight breeze as air is pushed from his lungs -- but only against his fingertip, not against the rest of his hand.
"Can you eat like this?"
John nods. "I can do everything. Nothing changes."
After several minutes of experimentation, Sherlock comes to the conclusion that it's as if John's body literally does not understand that it's been cut in two. He supposes that must be where the "magic" comes in -- somehow connecting the two separated ends of John's trachea to allow him to form words, his nerves to allow feeling, his vessels to allow blood flow, and so on.
The scientific implications -- the ability to observe healthy human organs without any of the trauma surgery would normally inflict -- are amazing. Which is why he can't let anyone else know, of course. Even his fingers are itching to slice into John's abdominal cavity and see what else he can observe.
"I'd like to cut you," Sherlock says; he winces inwardly at the way his words sound, but John doesn't seem to notice.
"That's fine. Anything you'd do in an autopsy is fine," John says. "God knows, I've done enough of it myself, prepping for practicums during school. Don't worry about sterilizing anything; I won't get an infection."
It's not as difficult as he'd thought it'd be, sliding the scalpel into flesh. John's bare skin is warm under his hand, warm and familiar and clearly alive, but that's where the normalcy ends. John's heart rate and breathing don't change. Blood doesn't well up at the incision point, and when Sherlock draws the blade away, John says, "No, deeper than that. You haven't even sliced through the muscle yet."
"Right," Sherlock says and cuts again, deeper this time and with more confidence.
And John splits open for him, glorious and beautiful and vibrant.
The first thing he notices is that the colors are different -- as expected, of course. John's still alive and his body more closely resembles that of a surgery patient than a corpse, while Sherlock's only had personal experience with the latter.
"Your organs are still functioning," he observes. He presses his fingers to John's stomach, tucked beneath his liver, feeling the way the organ shifts at his touch. It all glistens wetly and when Sherlock pulls his hand back, his fingertips are slightly damp but not bloody.
John makes a strange noise, shifting his weight on the table.
"Problem?" Sherlock asks but the expression on John's face isn't one of pain.
"I, no," John says, and shakes his head. "It doesn't hurt or anything, but it feels -- different."
"Do you want me to stop?"
"No, I don't mind," John replies, and lies still while Sherlock examines him, using only a scalpel and his bare hands. He doesn't dare remove anything -- not because he's afraid he'll cause harm, but because he isn't sure how he'd put it back.
He slides the scalpel higher, slicing through the muscles of John's chest until the blade scrapes against his sternum. He stops. "Your ribs are in the way," he says, daring to splay his hand on John's chest, feeling the warmth of his body. "I want to see your lungs."
"Cut the cartilage around the sternum, then push the ribs upwards and to the side," John directs expertly. Sherlock isn't sure if he's speaking from his considerable experience as a surgeon or his experience as... whatever he calls himself. An Addams, perhaps.
He does as John says. It takes more force than he expects to cut through the thick layers of connective tissue and pry John's ribs out of his way, but he manages eventually to do so. John's hand comes up to keep them from snapping back when Sherlock lets go. His lungs are a clean, healthy pink, expanding and contracting as he breathes. They're lighter than dead lung tissue, and spongy when Sherlock presses a knuckle to it.
But what catches Sherlock's eye is John's heart, dark red and pulsating in the center of his chest. Sherlock's seen plenty of human hearts before. This isn't the same at all though, because this one belongs to John.
When he reaches for it, it fits easily in his hand. Fist-sized, but John's hand is smaller than his. The muscle is firm and hard to the touch, beating strongly enough to pump blood throughout John's body. It is nothing like the limp, motionless things he's examined in the course of his experiments.
John's heart is in his hand, beating rhythmically against his fingers. Physically, John may very well be indestructible. The single scar on his shoulder implies otherwise but when Sherlock had asked, John had refused to give any details aside from a curt, "I got shot".
But he's still vulnerable, terrifyingly so. His secret is worse than drugs, worse than stealing evidence, worse than anything Sherlock's ever had to hide in the past. And John's trusting him with this secret, trusting Sherlock to know and study this last, hidden thing about him and keep it safe.
Sherlock wishes he could do the same. He wishes he had something he could tell John, something he could offer him and say, Here, so you can see me the way that I see you. Here, because I trust you with everything.
"Now I can say I've held your heart in my hands." It doesn't come out as light as he'd meant it. He expects a chuckle from John, perhaps followed by a comment he undoubtedly believes is witty.
When Sherlock doesn't hear either, he looks up to see John watching him with a strange, tender expression on his face. It's intimate, almost unbearably so, more intimate than even this, John's body laid bare and open before him.
"Didn't you know?" John's hand curls over the back of Sherlock's, warm and comfortable. His heartbeat quickens, fluttering between their clasped hands. "You've always been able to say that."
They end up in bed together after that, after Sherlock kisses John and knocks his head onto the ground by accident, and after they spend several minutes sealing the incisions in John's body.
It turns out John likes pain, just the hint of it, the scrape of Sherlock's nails on his back and shoulders. "Yeah," John breathes when he does it, arching into the touch, "Like that, harder, please."
And Sherlock likes John, likes the press of John's mouth on his own, likes the solidness of his body, likes the wondering awe in John's voice as he pushes into Sherlock's body and groans, "Christ, Sherlock, you're so tight."
When they're through, spent and content and curled against each other like puppies, Sherlock cards his fingers through John's sweaty hair and mouths the back of his neck. He asks, "Have you ever slept with someone who knew what you could do?"
John chuckles. "Considering the only other people who know are related to me by blood, no." He doesn't have to wait long for John to figure out what he's implying. "Why?" he asks, raising his head. "What are you thinking?"
Sherlock grins. "Well," he says. "I had several ideas in mind..."