Rebecca sat on the porch, trying to decide if today was a good day to kill again. He wasn't hers. The dog belonged to no one, as far as she could tell, and it never seemed to remember. In some ways, she wished she could trade places with the dog. No fear. No memories.

  It was in their backyard again. That's how she knew it didn't remember. She wasn't that lucky. She remembered all of it. From the day she'd first figured out what she was capable of to this moment, she was stuck with the weight of what to do about it. Her parents didn't get it. They thought acting as if things were normal was the answer. No one outside the three of them knew. It was for the best. It made sense. It really did. She was safe from the world this way. But was the world safe from her?

  The dog was brown. That was all she knew. It was better that way. If she paid more attention to it, looked deep into its eyes, or scratched its ears, there would be no way to know if she was ok. And she had to know. She'd gone more than 21 days not knowing at one point, and it had sent her into a panic, requiring her mom to take her to the hospital.

  The dog was close now. Her fingers twitched, knowing what came next. It was extremely hot outside, and the dog likely hoped to find some water. And she would give it water, but not because it was thirsty. What she was about to do horrified her. But it had been 7 days, and she wasn't sleeping well.

  She reached down and fumbled with a Ziploc bag hidden inside her tennis shoe, its plastic walls hugging black powder. It was insect repellent. The kind you spray on weeds. The kind that wasn't safe for animals to ingest. And this dog had already ingested so much. How many times had she fed it to him, she wondered, fingering the Ziploc. She was a monster. But she didn't feel like a monster. She felt nothing. She felt empty and irrelevant. And if her life was irrelevant, then how could a dog matter?

  Metal from an empty water bowl peeked through the grass in their backyard. It called to her to do it again. And then she was walking towards it, the dog finally registering her presence. The bowl was empty and hot. She carried it to the far right side of the fence and peered over into her driveway. Both her parents' cars were gone. Hers sat silently. Maybe if she got in it and blasted her favorite playlist, she wouldn't need to kill the dog. She could go get iced coffee with Mallory. Mallory would distract her.

  But Mallory didn't really know her. She wasn't aware that her best friend murdered dogs. There had been other animals before the dog, but he was so easy, and no one seemed to care he was missing. That should have bothered her. It was uncaring to know this about the dog and use it to her advantage, but she had to know. There was no way to fall asleep after so many days without knowing.

  The green water spigot sputtered as she turned its knob counterclockwise. A burst of clear sparkle shot from a hose lying close to the dog, and it jumped, but then circled back to examine the water. She picked up the hose and laid it inside the water bowl momentarily, then offered it to the dog.

  The dog, unafraid, lapped up the water gladly, tail wagging excitedly. She watched it drink, feeling nothing. And then she picked up the bowl and emptied the Ziploc bag into the bottom, watching the powder fall like pennies in a swimming pool.

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  The first time she'd done it, she'd stirred the water, making a solution, and then carried it around as if it were unsafe to have it around the dog. Which was accurate. It was unsafe. Deadly was the correct term. But even then, she'd known what would happen to the dog once she set it down, and she had done it anyway.

  Today, she simply set the bowl down in the grass. And the dog drank eagerly as expected. This part took about 45 minutes, so she went inside to make a grilled cheese. If she could find a more potent chemical, it wouldn't take so long, but somehow that seemed criminal. If anyone ever witnessed her kill the dog, they could ask that her phone or computer be searched, like on television, to prove she had planned it, searched for a chemical known to kill animals. So she stuck with insect repellent and ate lunch to pass the time.

  Bread, butter, and a single slice of cheese lay on the counter waiting to be assembled. Once that was done, she stared at the butter on the top of her sandwich. It was like the dog outside. Unaware that in seconds it would be exposed to a hot metal pan, its atoms ripped away from each other, solid sliding into liquid. She reached for her phone and turned up the volume on her AirPods. The dog would cry before it was over, and she didn't care for that.

  Balancing a paper plate on one knee and her phone on the other, she ate the grilled cheese and waited. What were they doing up there, she wondered? It was Tuesday. They had landed 9 Tuesdays ago. When she'd gone to Mars, it had been relatively boring, surrounded by adults, including her father, who rarely let her out of his sight. If time travel were a thing, she'd go back to the night they'd all sat around the dinner table at Guidos, an Italian restaurant downtown, her parents and grandparents toasting her incredibly brilliant luck at being the first kid to go to Mars. Now there were eleven kids on Mars. By now, they'd turned into monsters like her.

  An hour had passed, and she knew the dog was dead. This was the part that made her lightheaded. She stood, threw away the paper plate, and returned to the backyard. It was lying in the grass, silent and still. Her feet felt like bricks as she pulled them up and away from the earth, walking toward the dog now. In seconds, she would find out if she was ok.

  She kneeled beside the dog and waited briefly, not wanting to ruin the experiment. Seconds passed into minutes, and its brown fur lay unmoving. The dog was dead and facing away from her. She was thankful to be spared the foam around its muzzle. And then she began running her fingers through its fur, which was soft and warm. She ran her thumbs tenderly up and down its spine, wrapping her hands around its belly, massaging its hands and feet. It never took very long for the dog to come back.

  But in those few seconds, she was aware her life was in the dog's hands now. A complete flip of power that nearly flattened her each time. Because if he didn't come back, if she couldn't bring him back to life, that meant she'd lost the power Mars had given her.

  The dog was panting now, disoriented and confused. She scooped him up and held on to him tightly because she knew what he was feeling-a sense that something awful had happened, but she was unsure why or how to fix it. She kissed his face, still wet with saliva, its fur catching her tears.

  "It's ok," she whispered, rubbing the dog's head, its face nuzzling in the space between her neck and shoulders. "We're going to make it."

  And she believed that, even though the feeling wouldn't last because if and when she lost her superpower, she'd be just like every other astronaut they'd sent up, waiting for a diagnosis, waiting to die.