That's how Holt felt too. One mortal life was enough for him so long as he shared it with her and the rest of his family. If they all wanted to be immortal, he'd come along for the ride, but just him and Zinny.. it wasn't enough. It was all or none for him. He couldn't watch his baby grow old and die. No father could.
"When it's done," he teased, his eyes alight. "I told you I was working on it, which means it's not finished. If you heard it now, your nose would do that thing it does when you don't like something. Sure, you'd say it was great, but I'd know you were lying. I've got all your tells up here," he said with a tap to his head. "You're a terrible liar."