The slave lies on two stools, his head hanging over the edge, so his throat is fully exposed, right for to be sat on ;-)
Isabella enters the scene, steps over him and decends slowly her nice round ass on his throat.
His head is bended more with her weight on the throat, the pain-level rises and breathing is nearly impossible with the windpipe crushed in this way.
After some minutes, she shows some mercy and moves back on his face.