The slave is afraid the Mistress Ariel is going to fell off the chair, because of his clumsiness, but on the other hand it's very painful to have her pointy high heels deep in his skin on his face. So he tries not to move around too much, but all he wants is escaping the pain as Ariel steps on his face with her boots and pushes her heels into his flesh. She knows that she won't fell, but she enjoys his inner troubles showing.