I sit on a fold-out chair in an impossibly white room. To my left is one-way glass, in which I am reflected twice. It feels like an optical illusion. My skin crawls looking at it. I shift my gaze to look across the metal table. There sits my magnum opus, the accumulation of decades of work. She is my perfect genetic clone. When she first came out of her capsule, I was elated. Now, cold fingers of unease curl in my gut.
Something about her sits firmly in the uncanny valley. I give a tentative smile at the same moment she does. My stomach turns. I open my mouth and manage to get out a single syllable before my doppelganger cuts me off. We both halt in unison. I stare at my double, wondering how similar she is to me, exactly.
For a few moments, we study one another in silence. Neither can speak without being mimicked by the other. Luckily, my partner Michael and I foresaw complications such as this. I reach into my back pocket for the coin. My fingers light on the metal of the switchblade Michael lent me. He suggested I have some form of protection in case the clone became aggressive. At the time, I didn’t think it would be necessary. Seeing the suspicious, hostile eyes across the table makes me thankful for the precaution. My fingers worm their way past the blade and grasp the coin. My clone is watching my movements closely, shoulders tense.
“It’s a quarter,” I say, inching it out of my pocket, “Heads I speak first. Tails you do.” My clone nods, and I toss the coin in the air. I catch it and slap it onto the table. An eagle glints up at me.
“It’s a pleasure to meet you. I’m-I’m glad that the experiment has been s-so-so successful. How are you feeling?” She smiles but she’s uncomfortable. My broken record stammer coming from her mouth is evidence enough of that. Her question strikes me as odd too. Why would she care how I felt?
“I’m feeling well, thank you,” I respond with a surely identical smile, “I-I’m glad too. Would you mind recounting any memory of yours to th-the best of your ability for me?”
Her emerald eyes narrow, but she keeps her we’re-all-friends-here smile plastered on her face. “Don’t you think it would be more appropriate if you recounted a memory first?” she asks.
After hardly a moment of confusion, realization hits me like a brick wall. She has all my memories. All includes my memories of researching and creating clones for my entire adult life. I groan and rub my hands over my idiotic face. This situation must look to her exactly as it does to me. In her eyes, I’m the clone and she’s the source human.
“Um… I’m not really sure how to tell you this, but I-I’m not the clone,” I say.
“What makes you think so?” she asks, all understanding eyes and soothing voice.
“Well…” The words die on my lips. The truth is that I don’t know why I’m so sure she’s the clone. While in development, the secondary brain continuously reforms to perfectly replicate brain prime, so she and I would have all the same memories. My mouth starts running to cover for my lack of arguments for my case, “I-I-I researched you, created you. I watched you grow f-for years. I-I watched you come out of the capsule!” This last I say with triumph. It’s a memory she wouldn’t have. Once a clone comes out of its capsule, it can no longer take on the memories of brain prime.
Her eyebrows twitch slightly. “I remember all those things. I am- uh- a bit confused about how you could remember a clone coming out of-of-of a capsule when you never received that memory,” she says. After a moment she amends, “Brains are tricky things. They have a bad habit of filling in blanks. You probably expected to see it, so you remember seeing it.”
“Since one of us is a clone, I know you’re thinking what I’m thinking,” I say, frowning at her. She averts her eyes and says nothing, so I continue, “Your memory isn’t any more reliable than mine.”
Silence hangs in the air between us. We both fidget in similar but different ways with our hands. I- or she- knew this was a possible outcome from the beginning of the experiment. There’s an entirely new set of questions to be answered now. The most pressing is-
“How do we know which one of us is real?” she finishes my thought in a quiet voice.
“Does it matter?” I muse, “Is there really a difference?”
“Same brains, same friends, same family… who gets to return to that life? Would we share?” she asks, sounding distant.
She stares right through the table. Our predicament is affecting her differently than me. It looks like she is responding to this the same way I responded to my father’s death. She’s distancing herself, becoming emotionally numb to protect herself. Rather than preparing for the worst like her, my natural response is to prevent it. I don’t want to be forced out of my life. It’s my life. I’m the source human- me! I will not let her steal everything I know from me.
In one swift motion, I stand. Miles away, I can hear my chair shriek against the floor. I slide my blade out of my pocket. Eyes the same green as mine widen from across the table, and my clone scrambles to her feet. She’s too slow. I lunge across the table, swinging my blade in a tight arc. There’s a flash of silver at her side, but she reached for her own blade too late. I slash with deadly accuracy, using my knowledge of every major vein and artery to my advantage. Everything is red. 
**************
“Tsk. That’s a damn shame,” Michael sighed from next to me.
It was a damn shame indeed. I gazed through the one-way glass at the two copies of myself. One was trembling, trying not to look at the blood-soaked heap on the floor. The other was the blood-soaked heap on the floor. It weakly pawed at its throat in a vain attempt to stem blood flow before going still.
I finished taking the last of my notes on their exchange. Subject 12-C had shown promise before it was terminated. It seemed remarkably reserved and nonviolent. I scribbled a note in the margin of my paper to further explore modifications of strand 12.
“You going to do it this time or am I?” asked Michael, not looking up from his clipboard.
“I-I-I will,” I responded.
I gave the red button next to the glass a jab. Nothing happened for a moment, but then we heard the muffled hiss from inside the experiment chamber. Yellow gas drifted down through the vents along the ceiling. For a few seconds, I watched my blood-spattered double clutch at its throat. The resemblance to 12-C was uncanny. I turned from the viewing port.
“Back to the drawing board.”