The small body in the cage barely moved. With every labored breath, the dark red lump on its side swelled and subsided, almost imperceptibly. The low hum of the air circulator was the only sound in the room. The woman signed the chart beside the cage. Today's weight, food intake, notable observations. She wrote down the same words as yesterday, mechanically. 'Decreased food intake.' 'Reduced activity.' 'Tumor size increased by an additional 12mm.'
Having finished the record, she — Suhyeon — rested her hand against the clear acrylic wall. She felt no warmth through it. The white rat in the cage had its eyes closed. Receptor-7. That was the creature's official designation. Suhyeon had never once thought of the rat by that number. To her, it was simply 'him.'
Suhyeon took a small piece of apple from her pocket. It was against the rules. Her daughter had left it uneaten the day before. She pushed the finely cut apple piece through the narrow gap in the cage. The rat's nose twitched, just barely, as though it caught the scent, but it did not turn its head. The apple piece would slowly brown atop the sawdust.
Three weeks ago, the last molecules of the neuroblastoma in her daughter Yena's body had been transferred into this small creature. Quantum Transference Therapy — that was what the doctor called it. A technology that entangled Yena's tumor cells with the cultured cells of Receptor-7, then made the cancer's activity in Yena's body converge to zero while transferring all that entropy into Receptor-7. The doctor said the cure rate reached 98 percent. A miracle that 'lifted out' the cancer without ever putting a blade to her daughter's body, without ever searing her with radiation. Suhyeon had staked everything on that miracle.
She remembered the day the transference took place. Yena lay deep in sedation, and beyond the glass wall of the massive transference chamber, Suhyeon could see the biological containment vessel holding Receptor-7. The whole process unfolded in silence. Graphs rose and fell on the monitors, and then a green light came on — the signal that the transference was complete. While the nurse checked on Yena's condition, Suhyeon looked at the rat beyond the glass. For just a moment, it lifted its head and met her eyes. Small, black eyes, holding nothing at all. The instant she met that gaze, Suhyeon felt her heart drop. This was no mere lab animal. It was a being promised to carry her daughter's death in her place.
"Ma'am, you'll need to step out now. Care-room visits are limited to 30 minutes a day."
At the voice from beyond the door, Suhyeon lifted her head. A researcher was watching her through the gap in the doorway. It was Dr. Kim. He always wore the same expression, spoke in the same voice. Suhyeon nodded and stepped back from the cage. The door opened, and the sharp smell of disinfectant rushed in.
"How is the receptor doing?"
Dr. Kim asked as he checked the chart.
"It's not eating well. And... it looks like it's in a lot of pain."
"That's the expected course. The transferred tumor progresses at an average rate 1.7 times faster than the original. All the data remains within the normal range."
'Normal range.' The phrase lodged itself in Suhyeon's ear. It meant that the process of dying quickly was normal. Dr. Kim, perhaps reading the look on her face, added in a gentler tone.
"Yena's recovery rate is excellent. By next week she should be able to leave the sterile room. All of this thanks to Receptor-7."
Instead of answering, Suhyeon walked down the corridor. The seventh floor, where the care room was, and the twelfth floor, where Yena's hospital room was, differed even in the texture of the air. The seventh floor held a mixture of animals' faint musk, sawdust, and the shadow of death; the twelfth floor held only the smell of disinfectant and hope.
When she entered the room, Yena was drawing in bed. Just three weeks ago the child had been pale-faced, barely managing to breathe. Now color had returned to her cheeks. Seeing Suhyeon, the child broke into a wide smile.
"Mom! I ate all my porridge today."
"That's my girl. Well done."
Suhyeon stroked the child's hair. The once-thin strands had grown thick enough now. Every moment of the child's recovery was a miracle, and the cost of that miracle was being billed from a cage on the seventh floor. Yena held out her drawing. It showed Mom, Yena, and Dad standing beneath a big tree. And beside them, a small white animal was drawn in.
"This is a mouse. The good mouse that's making our Yena better."
The child had drawn a yellow crown on top of the mouse's head. Suhyeon took the drawing and could say nothing. Something hot seemed to lodge in her throat.
The next day, Suhyeon went back to the seventh floor. The mouse in the cage looked worse than it had the day before. The lump on its side had swollen past the size of a small marble to about the size of a ping-pong ball. It couldn't hold itself upright, lying on its side, breathing in shallow, labored gasps. The piece of apple she'd left the day before sat untouched.
Suhyeon pressed the nozzle of the water bottle with her hand and let a few drops fall. When she brought a drop to the mouse's mouth, a small tongue emerged and licked at the water, struggling. After a few licks, its head drooped.
"Does it hurt? Is it in pain?"
Suhyeon asked Dr. Kim, who was standing behind her. She hadn't noticed when he'd come to stand at her back.
"Pain responses have been observed. However, the receptor's nervous system differs from a human's, so we cannot definitively state that it experiences 'pain' in the way we understand it."
"Isn't there something like a painkiller? It looks like it's suffering so much."
"That's not permitted under the treatment protocol. Administering drugs could introduce subtle noise into the stability of the entanglement relationship. As a principle, external intervention is minimized for the sake of data continuity."
Dr. Kim's answer was, as always, clear, but to Suhyeon no sentence of it offered any comfort. Data continuity. For her daughter's perfect cure, this small creature had to endure its pain in full, to the very end. That was the precondition of this miracle.
"If the mother wishes, the procedure can be terminated early."
Dr. Kim said carefully. Suhyeon turned to look at him.
"Terminated — what do you mean?"
"Euthanasia. It's the standard procedure carried out when the receptor's vital signs fall below the baseline threshold, or when the tumor's metastatic state is judged to have crossed a critical point. At its current condition, the procedure would proceed automatically tomorrow or the day after, but if the guardian requests it, it can be moved up."
"If we do that... will it have no effect on Yena at all?"
That was the most important question. Dr. Kim paused for a moment. That brief silence froze Suhyeon's heart solid.
"I can't say for certain. The termination of entanglement means the termination of treatment. So far, 98% of the lesions have been successfully transferred, and Yena's body has recovered to nearly normal levels. But theoretically, to eliminate even the 0.01% potential risk that may still remain in Yena's body, the safest course is to maintain the entangled state until the receptor's life comes to its natural end."
He went on.
"Early termination would relieve the receptor's suffering, but it could raise Yena's chance of recurrence from 0% to 0.01%. Of course, 0.01% is statistically meaningless. Most guardians, in this situation…"
Dr. Kim did not finish the sentence. Suhyeon looked into his eyes. Those eyes said, the choice is yours. The hospital could only offer the safest path — it took no responsibility for the ethical anguish that lay along that path.
Suhyeon looked again at the rat in the cage. Its small body was gasping, spending its last remaining strength. The crowned savior that had rescued her daughter's life. And now, the sacrifice that must die in agony for the sake of her daughter's perfect future. Through the transparent wall, she quietly felt the weight of that small, fading breath.
Suhyeon didn't answer. She couldn't. Whether he took her silence as consent, or simply believed he'd said all there was to say, Dr. Kim gave a light nod and disappeared down the corridor. When the care room's door closed with a cold metallic clang, Suhyeon was alone once more. Alone with the small life in the cage. The number 0.01% kept circling in her ears. A statistically meaningless figure. But in a gamble staked on her daughter's life, no number was meaningless. It meant that out of ten thousand doors, exactly one led to hell — and Suhyeon did not have the courage to knock on that door.
She turned her back on the cage. She couldn't bear to look any longer. The small breathing sound seemed to reach out and hold her from behind, but she forced herself to ignore it. She stepped into the elevator and pressed the button for the 12th floor. As the numbers climbed, the air in the sealed compartment pressed down on her, heavier with each floor. The air of the 7th floor and the air of the 12th floor. Death and life. Despair and hope. In this iron box shuttling between the two, she was always a stranger.
The moment she reached the 12th floor, the air changed as if by some trick. It was full of bright lighting, brisk footsteps, the low murmur of nurses' laughter. She opened the door to the room, and her husband Minjun greeted her. He was sitting in the chair beside Yena's bed, reading a book while their daughter had just fallen asleep. Seeing Suhyeon, he whispered with a worried look.
"You're back? You don't look well."
"I'm fine."
Suhyeon set down her bag and looked into Yena's face. The child's face, breathing evenly in sleep, was the picture of peace. She gently brushed back the sweat-damp hair from her forehead. To protect this peace, she could do anything. She would gladly go through hell and back.
"The doctor came by today. Said Yena's condition is looking great. He thinks we might be able to prepare for discharge next week."
There was a joy in Minjun's voice he couldn't quite hide. Suhyeon managed a faint smile too. Thinking back on the past few terrible months, it felt like a dream. But when she thought of the price of that dream, the smile faded just as quickly. She looked out the window and spoke carefully.
"Today… I ran into Dr. Kim downstairs."
"Yeah? How's the rat doing?"
Minjun always seemed uneasy saying "Receptor-7." He called it "the rat," always — as if it were some third party that had nothing to do with him.
"Not good. Its condition's gotten a lot worse. But… he said they might be able to end the procedure early. Euthanize it."
At that, Minjun's face brightened.
"Really? That's good. The poor thing must be suffering. Of course we should do that. It's been through all this because of us — the least we can do is make its last moments easier, don't you think?"
His words were kind and reasonable. They were the same words Suhyeon had repeated to herself every day. But now that the moment of decision had actually arrived, it wasn't so simple.
"But… if we do that, apparently there's a 0.01% chance of relapse for Yena."
Minjun fell silent for a moment. He furrowed his brow, repeating the number under his breath.
"0.01 percent?"
"Yeah."
"That's it? That means it's 99.99% safe."
Minjun let out an incredulous little laugh.
"Honey, that's basically nothing. Why are you agonizing over a number like that? Of course we should euthanize it. Leaving a living creature to suffer for days longer over some negligible probability — that's just cruel. We don't need to become monsters to save our Yena."
At his firm words, Suhyeon felt something go cold in her chest. Monster. Maybe she already was one. For the sake of her daughter's perfect safety, she was looking away from a small creature's suffering. But to her, 0.01% wasn't just a number. It was the size of a nightmare they might have to live through all over again.
"You don't understand. What that one small probability meant to us. Don't you remember, when Yena was first diagnosed, the doctor talking about survival odds? We staked everything on a sliver of a chance to get this far. And now… I don't want to create even a 0.01% risk again. I can't do it."
Suhyeon's voice came out trembling. Minjun looked at her as if he couldn't understand her at all. An expression of pity and frustration, tangled together, flickered across his face.
"Suhyeon. That's not reason talking — that's feeling. I know you've grown attached to that rat, going up to the seventh floor every day. But we have to look at reality. What matters most to us is Yena. Yena's health, Yena's future. Right now you're not looking at Yena — you're looking at that rat."
"No! I am looking at Yena. I'm hesitating precisely because I'm looking at Yena's perfect future!"
As their voices rose, Yena, asleep, stirred faintly. Both of them fell silent at once. Stillness settled over the room again. Only the soft rhythm of Yena's breathing and the city noise beyond the window could be heard.
Minjun let out a deep sigh and rose from his seat. He gave Suhyeon's shoulder a light pat.
"You make the decision. You're the one who faces it every day. But don't drag it out too long. For your sake, and the rat's, and everyone's."
He looked in on Yena's face for a moment, then said he'd get some air, and left the room. Left alone, Suhyeon sank into the chair as if collapsing. Her husband was right. Maybe this was a matter of emotion. That day the transference took place, those small black eyes she'd met through the glass wall. The wordless promise of that moment, when she had taken her daughter's death entirely upon herself. All of it held her fast by the ankle. She quietly took her sleeping daughter's small hand. A warm, soft heat passed into her. To protect this warmth, down on the seventh floor, a small body was growing cold. Suhyeon closed her eyes. The weight of the choice bore down on her, through her whole body.
How much time had passed? The hospital room door opened quietly and Minjun came back. In his hands were two warm cans of coffee. Without a word, he pressed one into Suhyeon's hand, then sat back down in the chair beside Yena's bed. He said no more about euthanasia, but his silence pressed on Suhyeon in a different way.
"I'm sorry. I was too on edge."
Suhyeon broke the silence first. Minjun shook his head.
"No, I'm the one who didn't understand your heart. I didn't consider what you see every day, what it does to you. I'm sorry."
Their mutual apologies seemed to lift the heavy air in the room a little, but they solved nothing at the root. That night, Suhyeon couldn't sleep. Once she'd confirmed her husband and daughter were asleep, she slipped out of the room like a ghost. Her feet carried her to the elevator on their own, and her finger pressed the button for the seventh floor without hesitation.
The seventh floor at night was steeped in a darkness and silence deeper than daytime's. Only the dim glow of the emergency lights lit the corridor. The care room door was locked tight. Peering through the glass, everything beneath the cages' minimal lighting seemed frozen in place. Suhyeon leaned her forehead against the cold glass. Just then, she sensed movement inside.
It was Dr. Kim. Instead of his white coat, he sat before the monitor in casual clothes. Spotting Suhyeon, he came over with a startled look and opened the door for her.
"What brings you here at this hour?"
"I couldn't sleep… I just…"
Suhyeon couldn't finish the sentence. Dr. Kim seemed to read everything from her face. He hesitated a moment, then motioned for her to come inside.
"Would you like to come in and see, just for a moment? I happened to be checking on its progress."
The rat in the cage now seemed to hardly breathe at all. Every so often its body gave the faintest convulsive tremor, and that was all. The tumor at its side had swollen taut, as if about to burst through the skin, its surface glistening.
"As you can see, its vital signs will soon drop below the critical threshold. It probably has only a few hours left."
Dr. Kim spoke matter-of-factly. He pointed at his monitor. On the screen floated a dense array of graphs and numbers, along with a three-dimensional image showing the inside of the rat's body.
"This is the data stream representing the entanglement state. It shows how the two organisms are connected at the quantum level."
One complicated line was pulsing faintly. He zoomed in on a particular section of it. "This waveform is Receptor-7's pain index. As you can see, it keeps crossing back and forth over the threshold. And this one, over here, is Yena's bodily stability graph. It's a perfect flat line. In effect, that pain is what's holding up this calm."
It was brutal proof of the very principle behind the miracle. Suhyeon couldn't tear her eyes from the screen. This was the scene in which her daughter's perfect peace was being traded, in real time, for that small creature's extreme suffering. Dr. Kim's finger hovered over the keyboard.
"If I press Enter here, just once, it's all over. The entanglement is forcibly terminated, and the receptor, without pain, immediately—"
His finger stayed frozen above the keyboard. He looked at Suhyeon. His eyes were no longer those of a detached researcher. They, too, were the eyes of someone who understood the weight of this miracle.
Instead of answering, Suhyeon looked back and forth between the monitor and the cage. On the screen, her daughter's life graph, drawing its perfect flat line, and the rat's pain graph, thrashing wildly, ran on side by side. A cruel law of equivalent exchange, in which one being's agony gave birth to another's peace. Only now did she feel she understood the true nature of this miracle. It was not simply a technology for 'removing' cancer cells. One creature's calm was growing by feeding on another's convulsions.
The Enter key. That one small square of plastic could stop the scale from tipping. It could halt the transfer of pain, could sever the link of entanglement. Even if the price was living forever after with that 0.01% of anxiety. Maybe her husband had been right. Maybe this was never a matter of reason, but of feeling. Those small black eyes she'd met through the glass wall of the transference chamber. The 'good rat' wearing a yellow crown in her daughter's drawing. Preserving at least a shred of dignity for that being. She thought of the yellow crown in her daughter's drawing.
She could not let their savior meet an end like this. The sacrifice made for her daughter's life had already been enough. What remained now was only the meaningless prolonging of suffering. Suhyeon made up her mind. She stepped past Dr. Kim toward the keyboard. Startled, he tried to say something, but seeing the look on Suhyeon's face, he closed his mouth. Quietly, he stepped back to give her room.
Suhyeon's finger trembled faintly in the air. She looked one last time at the small body inside the cage. Little one, it's all right now, she whispered silently in her heart. Her finger slowly descended and stopped over the Enter key. And then, she pressed it.
The turbulent red waveform seemed to seep away into the screen and vanish. Only a long, still green line remained. Inside the cage, the faint tremor that had shaken the mouse's frail body stopped completely. The small body settled at last into perfect stillness. Death was astonishingly fast, and quiet. Dr. Kim spoke, low.
"Entanglement relation: terminated."
Suhyeon nodded without a word. No tears came. The weight that had pressed on her shoulders was gone, and for the first time she could breathe deep. She gave the cage a small bow of the head, then turned away. There was no longer any reason to stay here.
As the elevator carried her up to the twelfth floor, she watched blankly as the numbers changed. The air of the seventh floor emptied completely from her lungs. When the doors opened on the twelfth floor, bright, warm air met her, carrying the familiar smell of disinfectant. Her own face, reflected in the elevator's metal wall, no longer looked like a stranger's.
When she opened the door to the room, Minjun was curled up asleep on the sofa, and Yena was still breathing softly, evenly, in her bed. Suhyeon quietly went to her daughter's bedside. On the table by the pillow lay a drawing Yena had made: a great tree, Daddy, Mommy, and Yena. Beside them, a white mouse wearing a little yellow crown was smiling.
Suhyeon gently ran her fingertip over the crowned mouse in the drawing. A faint trace of crayon oil came away on her finger. She took her sleeping child's small, warm hand and held it softly between both of hers. She thought she could feel her own pulse beating faintly at the child's wrist. It was warmth of 99.99 percent.
