He sounds a quiet "oh?", as that gets him thinking. Truthfully, he hadn't a clue how any of this train-travelling actually worked, but the word portal has come up before in other conversations. He thought portals were another way of getting from one place to another, which--sure, it still is, but it sounds more complicated than that.

"You don't have your dead people on the same planet...uh, in the same realm as you?" Really complicated.