I think my T and I mirror each other at times. I think we mirror others in our lives too. It can be quite natural. I think it is a good thing. It helps two people feel close. I don't do it to mock people or manipulate them. I would think a T would like it if he and a client were attuned enough that they were mirroring each other. I don't do it with crossing legs and such, but more with pacing, non-verbal noises, mood, affect, and also what I say in response to what he has just said. There are times I cannot do it though, and it is usually when T is at a more extreme mood. I am better when we are "in the middle" somewhere.