It's not totally unexpected to see the indecipherable writing, Five got enough of a sense of how he took notes from the farmhouse, but he also hasn't spent a lot of time attempting to read it. So he listens instead. That he's suddenly decided to mix his magic with Karsa is an unexpected choice, and it's even more unexpected that she shared that with him, but it might reveal something. He still hasn't figured her out, and she tends to get his temper flaring before he ever makes it very far.

If nothing else, he solved the mystery of what they've been talking about. Though he still hasn't grasped magic enough that it's clear what that means by 'thralling' and how that relates to the quartz, or if he's even talking about the same thing he started with.

"And if you succeed, what are you trying to use it on?" He hates having to ask such basic questions, but he did offer to teach him before, when he was helping his sister. He's learned what subjects he'll speak openly about.