Jane wears shoes with high-heels, the heels are not very spickey, but the edges of the heels are sharp.
She steps on her slave's belly and begins to test how far the heels are digging in his flesh, if she shifts her weight to the heels.
The slave moans because the heel goes deep in his fat belly and they leave nice sings on his skin.
She also walks toward his face and steps on his head, she isn't that inhuman and steps with the heels on his face, she's only nearly so inhuman, so the slave thinks she would step on the face and damage it.
But she sits down and takes place on his soft belly, using his face as her footstool.
Now she can play with the sole and heels the face-squeezing game.