"Fucking hell, Sarah," Mitchell said. "I guess I'll just stop talking. Just…" He made a growling sound of frustration.
"You know how much I hate it when you curse at me," Sarah said. "You can't argue without cursing. I hate it." She sighed. "And that weird growling sound. It makes me afraid you're going to hit—"
"Afraid I'm going to hit you, yes," Mitchell interrupted. "Because that's ever happened in the past. I can't just be angry at how fucking irrational you are all the goddamn time; no, I must be abusive. Jesus Christ, Sarah."
She was crying already. Mitchell felt terrible, but he wasn't willing to apologize yet. This trip was already a nightmare, and Mitchell didn't think the hike would be much better. He thought about turning around, decided against it. May as well give her some time to calm down, he thought.
They reached the parking lot for the trail, sullenly put on their packs, and carried on. After an hour or so, Mitchell finally turned to Sarah. "Look, I'm sorry. For the way I acted."
"I…" Sarah sighed. "Yeah, I'm sorry too. I know how stressful it can be, doing as much work as you do. You really do need to work on your anger issues, though—"
"I know," Mitchell said.
"—and also your interrupting issues," Sarah said, frowning for a moment. Mitchell apologized again.
They held hands the rest of the way along the trail, stopping to sit on a rock for a moment. Sarah got out her canteen and took a drink, passing it to Mitchell. I really do love him, she thought. I just wish he could be—
Sarah saw something peeking its head out of the woods. Is that a monkey? she thought. What's it doing out—
The monkey dashed along the ground towards them. "Mitchell! Look out!" Sarah screamed. Mitchell turned and looked just in time to see the little monkey bite him on the hand and dash off into the woods.
"Ow, goddammit!" Mitchell yelled. But the bite didn't hurt as much as he felt like it should, so he composed himself. She already thinks I have anger issues, he thought. No reason to act crazy now, not when we're patching things up. "Aw, that was weird," he said.
"Oh my god, are you okay?" Sarah asked
"Yeah, yeah, it's cool," Mitchell said, playing off the pain. "Dude had little teeth or something. Eh, I'll be all right."
Sarah packed the bags back up; Mitchell did the same. They began walking back.
Half an hour of far more pleasant conversation followed. Halfway back to the parking lot, Sarah paused a moment. "Do you smell that?" she asked.
Mitchell sniffed. "I don't smell anything."
"Of course you don't," Sarah snapped, "you never smell anything. Jesus, I think you have a tumor or something. Same way you can't hear anything, either. At least not anything I say." Sarah shook her head and walked around for a minute, sniffing the air.
"God, sorry," Mitchell said, recoiling slightly.
Sarah sighed. "It's disgusting. I don't know how you could possibly not smell that." They kept walking.
"Oh, god," she said after a while. "I know where it's coming from. It's you. I'm sure of it. What is that?"
"Hmm?" he asked.
"Jesus, you really don't listen, do you?"
"Oh, not this again," Mitchell huffed. "What is it now? Am I not picking my feet up enough? Did I pick my nose? Do I have too many zits? Did I bring the wrong books? Did I forget what your favorite purse looks like? Did the food I brought not have enough green vegetables? What do you have to complain about now, for fuck's sake?" Mitchell realized he'd gone too far, took a step towards Sarah. "Oh, shit, baby, I'm sorry, I didn't mean—"
Sarah slapped Mitchell directly across the face. "You pissant piece of shit, don't you ever speak to me like that again!"
Mitchell was shocked, and in a considerable amount of pain. He rubbed the spot on his face where Sarah slapped him; it had come back with a spot of blood on it. He looked at Sarah and was shocked. She looked nearly crazed with anger.
Sarah charged at him; Mitchell didn't know what to do, so he started running away. He dropped his pack on the ground so as to run faster. Sarah was close behind him, though; her time at the gym left her in better shape than he was.
Mitchell heard a rustling in the woods beside him, then saw a form emerge. A dog was running next to him. Not even a big dog, maybe just a terrier. Mitchell didn't think much of this until the chipper-looking dog launched itself at him, growling and snarling as though it were rabid. The thirty-pound terrier brushed past Mitchell, its teeth nipping at Mitchell's leg before falling to the side. What the fuck is going on? he thought.
He wasn't looking at the trail closely enough. A group of small animals were coming at him, mostly squirrels and stray cats. Startled, Mitchell tripped and fell to the ground, huffing. The squirrels began nibbling on his ears as soon as they reached him, while the cats clawed at his hands.
Sarah was close behind. Mitchell fought to throw the animals off of him, clawing his way forward, but Sarah was too fast. She dove onto his back, knees first, shoving him to the ground with her weight.
"You piece…of shit…" Sarah snarled, beating on the back of Mitchell's head with the bottoms of her fists, "moody….insecure…pussy…asshole!" The blows kept raining down. Mitchell was dizzy, his blood all over the ground now. He was barely holding on to consciousness. "I fucking…hate you…you son of a bitch! Just…fucking…die!"
Sarah found a palm-sized stone on the ground nearby. The terrier caught up to the group and started biting at Mitchell's ankles. That was the last feeling Mitchell noticed before the rock smashed into his skull the first time. He didn't feel the last twenty-six times.

Researcher Kim was sitting in front of his computer, considering the information in front of him. There were six murders now, all unrelated, all in wooded regions of the Southeast United States. All committed by people with no history of violent crime, often simply people who were near the victim. Hell, in two of the cases, multiple people all joined in, beating or clawing or kicking the victim to death. And in every instance, all signs pointed to a temporary yet total psychotic break. They all simply decided to kill somebody near them.
Ten people do not "turn crazy" all at once. They don't murder a man for no reason. Their official cover stories involved drugs, gas leaks, the usual, but Kim wasn't the only one who knew that didn't explain things. Kim agreed with his colleagues who forwarded him the information; something anomalous was going on. He just had no idea what to do with that knowledge. He had no idea how to find…whatever this was.
He heard a rustling sound behind him, like paper on tile. Rubbing his eyes (how is it already past midnight, Kim thought), he turned to look.
A large manila envelope was just in front of his door. Kim walked over, opened the door, looked back and forth down the long hallway. Nobody.
He closed the door and grabbed the envelope. Inside he found a batch of twenty photos, a printout of a Wikipedia article, and a single sheet of paper with some words scrawled on it.
He looked at the photos. He was shocked to recognize many of them, all photos of the victims he had been looking at only a few minutes ago. First he saw Mitchell Rosenberg, the most recent victim, covered in bite marks and lying with his head smashed in from behind. Next was another photo, much closer, showing Mitchell's hand. A circle was drawn around one bite in particular.
The rest of the photos were the same; first, a victim, then, a single bite. Kim's knowledge of forensic science wasn't needed here. Anybody would have recognized it. Each victim was covered in bites from small animals, but they were usually different animals. This bite, however, was exactly the same on every single victim. Many of the photos were of victims Kim didn't recognize; he assumed they were new.
He put down the photos and picked up the single sheet of paper. After some time, he was able to make out the scrawl. It was an address somewhere in Tennessee, no place Kim recognized. Below that read simply "LOOK IN THE BARN. BRING MASKS."
Kim, confused, put the paper on top of the photos and looked at the Wikipedia article:

The Philippine tarsier (Carlito syrichta), known locally as the kupal in Cebuano/Visayan and mamag in Luzon…

He skimmed the article and began typing a message to his supervisor.