Oh, he has plenty of experience with defies mortal convention. But that category of being— which is to say, eldritch abomination— doesn't generally map onto reality like this. This doesn't align tidily with any of the rules he's used to, which is damned inconvenient.

"If you know something I don't about immortal beings, I would love to hear it." This is said as though genuine, just as mildly spoken as the rest.