We can't see her face, but this tells you they are seeing something completely unexpected and bizarre when Hillary's head and face begin bobbing around.
The woman on the left is obvious, she is bugged out by what she sees. As the recording progresses, it is clear this screenshot isn't just a frozen frame at the "wrong" time for the person. She goes from recording mode to "WTF" mode as she recoils from Clinton.
It is remarkable footage. As you watch the woman in the middle and the man on the right, they progress from being in the "recording our candidate" mode, to puzzlement, then back to "recording our candidate: mode.
The one on the left though is completely weirded out. Wonder what she saw. (maybe the forked tongue accidentally slipped out past her lips?"