But that wasn’t all. The shorter, central branch of the triple fork, the “head,” had been shaped. Rubbed, until it was rounded and smooth. Until it was shaped like a head, not just a broken stump of reef coral. And on all the branch ends, the same had been done. The broken edges were smoothed. But even that was not all: On the worked surface of the “head” were three indentations, chiseled into the surface of the coral. Three horizontal grooves, two smaller and one larger, positioned to suggest eyes and a mouth.

“The octopus could have found it on the beach or somewhere else. The finishing of it could have been done by one of the islanders,” Dr. Mínervudóttir-Chan said.

They had moved one of the lobby tables out onto the terrace, near the algae-clogged pool, at Dr. Mínervudóttir-Chan’s insistence, so she could “work in the daylight, at least. Think in the open.”

The outside, the sunshine, was Dr. Mínervudóttir-Chan’s home, the way for Ha the underwater was home. Arnkatla was always dressed as if she were about to go for a run, or had just come back from one. And when she was not absorbed in one of the terminals, that was exactly what she was doing: running the roads and paths of the island.

“Yes, that is true,” Ha said. “We can’t conclude the octopus made this. But at the least, it is a manuport: an object moved purposefully from its original context because it had importance or significance. We have proof of that. The octopus pushed this piece of coral into my mask. It gave it to me. At the least it made a connection between the shape of the object and our shape, and it wanted to communicate that connection. But I think it’s possible it made the object itself.”

“A leap of logic.”

“Not such a huge leap,” Evrim said. “Ha and I found marks all over the tide pools on Bay Canh Island, where one of the rangers was murdered a few years ago. The marks were evidence that the octopuses have been using tools to scrape shellfish off the surface of the rock.”

“And those tools weren’t made by humans?”

“Look,” Ha said, “the skepticism is valid, but we also can’t ignore what is right in front of us. You see the submersible video of my interaction with the creature.”

On the terminal, the clip was paused at the moment when the octopus was pulling aside Ha’s mask. The edge of the coral figure was visible, wound in the tip of its arm. Ha had not known the cloaked submersible was there. But I should have known: Where is Altantsetseg not spying on us?

The submersible had captured everything from the moment Ha entered the water to the moment the octopus darted away.