The slave is trapped in the foor with a hole for his face, he cannot turn the head or move the face away... a perrfeect victim for Isabella.
She wears flat boots and steps first on his chest, then on his hands, then carefull on the face.
Soon she gets more confident with the face under her soles anincreases the facetrampling.
She cares that she concentrates all her weight on the small face or sometimes she steps with both feet on it.
Yes the boots are only flat, but with a hard sole, so the face gets seriously deformed and crushed.