The slave is trapped in the floor with a hole for his face, he is fixed cannot turn away, he must hold his face every time upturned.
First Jane plays a little bit with her feet on the face...
Then she stands up and steps on the presented helpless face.
Her first steps are carefull, not with to much weight, then she increases and steps with more weight on him.
The face gets seriously crushed and flatened, when she steps and walks with all her weight on it.