It's the transducer in the face. It irritates them. Some babies like mine will actually try to push the transducer away. My first son did at the 30 week ultrasound. lol
My baby girl look mad lol she is so beautiful I can't wait to meet her.
Babys can cry in the womb, they imitate the same face as if they were to cry outside of the womb. Sometimes i wonder if my baby cries in there!
Yup I would say its just baby moving his facial muscles - he can't be sad all snuggled up and warm in your belly :)