The secret thing. Yes, Martin has noticed that he knows things about people now that he wouldn't have thought possible. Also, he seems to have an innate sense as to the location of bone charms and runes-- both abilities he's not keen on sharing, especially with someone like Billie.

"I don't remembering agreeing to tell you anything."

This was something the Outsider had decided upon. Like bringing the former High Overseer back as a talking head.

Fucking whale gods.