I do have conversations with T in my head. Sometimes before a session, I will think about the things I want to say to him, and how he might react.
I mainly do it between sessions when I want to call/e-mail. If I need his viewpoint/advice/support, I can usually imagine pretty clearly what he will say in response to what I need to say. And then I don't need to call. If I just need to *connect*, I'll still call/e-mail.
I do it IN session a bit too. I'll think "well, I'm going to say x and T will say y" so I'll tell him "x" and then add "DON'T say y!" Gotta keep him on his toes, you know!

