The thing about talking to Cortana is that, most of the time, she has no visible avatar for the Chief to give meaningful looks to. It means he has to talk.

"Sounds like someone we knew," he says. It's flippant too, but loaded with worry. That's far too close to the Gravemind for comfort, and while he hasn't openly discussed it with her, he knows that facing off with the Flood hivemind hurt her badly. This can't have helped, and the Chief's concern hangs between them, the question of her welfare unspoken but obvious.

They haven't been friends for a long time, by most standards, but the circumstances have strengthened it more than years ever could. He respects Cortana, and will give her a chance to come around to it herself before he'll push the issue outright.