He pretends that the pause in his step is because he's still tired, aching from the regeneration overtime.

"Sharp as a tack, Jack," he says, rolling his eyes without actually doing it. It sounds like he's just mocking him at first, but his tone grows somber. "Who knows, maybe you'll all figure it out. If you make it off this moon alive."

Coming from him, it probably sounds like a low-key threat, but it's hard to tell for now as he slowly walks away from him. He obviously can't leave the cruiser, but anywhere away from here will suffice.