My T has done that too. Maybe more in the early part of my therapy. My response has varied from silent chuckling because I realized it was mirroring (and I relate that to mothers and infants) or internal eyerolling when I notice and it seems exaggerated and very 'not her'.

At one time there were sessions where she kept getting up and going outside the room very briefly to adjust the thermostat that is right beside her door. Several sessions she did this a few times during the session and so I asked her if she was "going away and coming back", like the toddler fingerplay of "Two Little Blackbirds (sitting on a hill)". But she said she wasn't that clever. I was reading a lot about attachment and child development at the time so that's where my mind was.