She took a breath. "We're not the best either, apparently. The best never got off the ocean floor."

"And it's in me now? I'm some sort of Patient Zero?" Scanlon shook his head. "No. It's impossible."

"Yves—"

"It's just the deep sea. It's not outer space, for God's sake. There's currents, there's circulation, it would have come up a hundred million years ago, it'd be everywhere already."

Rowan shook her head.

"Don't tell me that! You're a fucking corpse, you don't know anything about biology! You said so yourself!"

Suddenly Rowan was staring directly through him. "An actively maintained hypo-osmotic intracellular environment," she intoned. "Potassium, calcium, and chlorine ions all maintained at concentrations of less than five millimoles per kilogram." Tiny snowstorms gusted across her pupils. "The consequent strong osmotic gradient, coupled with high bilayer porosity, results in extremely efficient assimilation of nitrogenous compounds. However, it also limits distribution in aqueous environments with salinity in excess of twenty parts-per-thousand, due to the high cost of osmoregulation. Thermal elev—"

"Shut up!"

Rowan fell immediately silent, her eyes dimming slightly.

"You don't know what the fuck you just said," Scanlon spat. "You're just reading off that built-in teleprompter of yours. You don't have a clue."

"They're leaky, Yves." Her voice was softer now. "It gives them a huge edge at nutrient assimilation, but it backfires in salt water because they have to spend so much energy osmoregulating. They have to keep their metabolism on high or they shrivel up like raisins. And metabolic rate rises and falls with the ambient temperature, do you follow?"

He looked at her, surprised. "They need heat. They die if they leave the rift."

Rowan nodded. "It takes a while, even at four degrees. Most of them just keep way down in the vents where it's always warm, and they can survive cold spells between eruptions anyway. But deep circulation is so slow, you see, if they leave one rift they die long before they find another." She took a deep breath. "But if they got past that, do you see? If they got into an environment that wasn't quite so salty, or even one that wasn't quite so cold, they'd get their edge back. It would be like trying to compete for your dinner with something that eats ten times faster than you do."

"Right. I'm carrying Armageddon around inside me. Come on, Rowan. What do you take me for? This thing evolved on the bottom of the ocean and it can just hop into a human body and hitch-hike to the big city?"

"Your blood is warm." Rowan stared at her half of the table. "And not nearly as salty as seawater. This thing actually prefers the inside of a body. It's been in the fish down there for ages, that's why they get so big sometimes. Some sort of— intracellular symbiosis, apparently."

"Fine. What about the, the pressure difference then? How can something that evolved under four hundred atmospheres survive at sea level?"