My T lets me know sometimes what emotion he feels. I think he is mirroring to me how to name emotions. "I feel sad that I missed you saying that in session last week." or he will say "I feel angry about what your father did to you."
Sometimes I can see if I push his button about something. He shifts and withdraws emotionally to keep himself safe. Then I appologize as soon as I realize what is going on and he comes back :-)