What was the party trick of Stef's that impressed Van so much the first time they had sex? (I have a theory, but, go on, surprise me).

Possibly related: On the way back from Forst Reach, Stef thought he might have shocked or offended Vanyel...what had he done with Van that would make him wonder that?

(I'm okay with these being taken as the same prompt or two seprate prompts).