The Other Brain

The jar on the counter was bubbling, and Soren was the only one watching it.

"It's breathing," he said.

Maya looked up from her grandmother's tablet. "It's not breathing. It's the bacteria. They eat the cabbage sugar and burp."

"That's basically breathing."

Grandmother Pilar called from the next room, where she was untangling yarn. "Don't open it. Three more days. The little ones are working."

"The little ones," Soren repeated. He leaned close to the glass. Tiny silver beads climbed the inside and let go at the top. "There are billions of them in there. And we just leave them on the counter like a pet rock."

Maya had gone back to the tablet. She'd been reading an article her science teacher sent, the kind with too many words before it said anything. She scrolled, scrolled, then stopped.

"Soren."

"What."

"Where do you think serotonin is made?"

He thought about it honestly, the way he did everything. "The brain. It's a brain chemical. The happy one. It's in the brain."

"That's what I'd say too." She turned the tablet toward him. "It says here ninety percent of it is made in your gut. Not your brain. Your gut."

Soren read it twice. He always read things twice. "Ninety."

"Ninety."

"That can't be a typo. Typos don't say ninety percent." He sat down slowly. "So the chemical that's supposed to live in your head. Most of it gets built down in your stomach. By cells. And some of it," he glanced at the jar, "by the bacteria living down there."

Maya was already ahead of him. "The same kind. As in the jar."

"Not the same exact ones."

"Cousins."

"Cousins," he agreed. He pulled his notebook out of his backpack and uncapped the pen. He drew a person, then a circle low in the belly, and wrote a number inside it. He looked at the jar, looked at the drawing, and did not say anything for a while.

Maya watched the beads climb the glass. "How many bacteria are in a person?"

Soren checked the tablet. He read it, and then he laughed, but not a funny laugh. A careful one. "It says about the same number as your own cells. Maybe more. They're not even outnumbered. It's basically a tie."

"A tie." Maya stood up. She walked to the jar and put her face right next to Soren's, both of them staring into the bubbles. "So when I'm me. When I wake up and I feel okay or I feel rotten. Some of that feeling. Is being made by something that isn't." She stopped.

"Isn't you," Soren finished.

"Isn't only me."

Grandmother Pilar came in then, drying her hands, and saw the two of them nose to nose with a cabbage jar. "What."

"Abuela," Maya said, not turning around. "When you were sad. After Abuelo. You told Mom you couldn't eat."

Pilar's hands went still on the towel. "That's a strange thing to bring up at the counter."

"Was it that you weren't hungry. Or was it the other way."

"What do you mean, the other way."

Maya turned around. "What if not eating changed who was living in there. And that changed the chemicals. And the chemicals were part of the sad." She said it fast, all in a rush, then looked worried she'd said too much.

Pilar didn't laugh at her. That was the thing about Pilar. "I don't know, mija. The doctor never said anything like that." She folded the towel. "But the soup helped. My mother's soup. I always thought it was the remembering. Maybe it was the soup."

She went back to her yarn, leaving the question on the counter with the jar.

Soren was writing fast now. "Okay. Okay. Think about this. People take medicine for their mood. Pills. The pills work on serotonin, right, the brain one."

"Right."

"But if ninety percent of it is made down here." He tapped his belly. "By cells and by bacteria. Then somewhere right now there are scientists who get to ask. What if you changed the bacteria instead."

Maya's eyes went bright. "Like editing the jar."

"Like editing the jar. Pick which little ones live in there. Pick the ones that make the chemical you need." He stopped writing. "That's a real thing people are trying. It has to be. You can't read this and not try it."

"I wouldn't be able to not try it," Maya said.

They stood there, both of them, with the enormous quiet thought of it. That there was a second brain, sort of, a wet and breathing one, made of strangers who weren't strangers, living in the dark of every single person, mixing up the feelings nobody could see.

"Soren."

"Yeah."

"Everybody on the bus this morning. Everybody at school."

"Yeah."

"Each one of them is carrying a whole jar around. Billions. Making chemicals. And none of them know." She pressed her hand to her own stomach, not to feel anything, just to be sure it was there. "There's a whole second population of me. And it's been keeping me company my entire life."

Soren looked at his drawing. The little circle. The number. He added one more thing, very small, in the corner of the page: a tiny jar, with beads rising out of it.

"Three more days," he said.

"For what."

"Until we can eat them." He grinned. "And then they're us. They cross over. They start working."

Maya looked at the jar like she'd never seen a jar before. A silver bead let go of the bottom, climbed the whole height of the glass, wobbling, slow, and burst at the surface without a sound.

Neither of them said anything.

The next bead was already rising.