What does Imogen do wrong?

She screams

Again and again you slash the vicious quirt into your student's silken flesh, building a crescendo of agony breathtaking in its intensity. **** sobs and wails alternate with periods of inaudible speech, as if Imogen is praying or trying to give herself encouragement, writhing helplessly beneath your relentless onslaught.

The quirt is light, but the **** of impact is still sufficient to test Imogen to the limit and as the skin begins to peel from between her shoulder blades, a particularly effective lash rips a howl of unbearable anguish from her throat.

"Oh, no! I'm sorry. Please, no."

"You know what this means," you say, solemnly. "If you can't remain quiet, I'll have to take you downstairs. You have taken nine lashes so far, so the remaining eighty-seven double to one hundred and seventy-four."

Imogen lets out a wail and starts to sob so wretchedly that both books fall from her hands.