From the web site:

"The sister reads for her university exam. She's already tired, her thoughts wander over the pages. The brother, having watched her for some time, joins her with his personal aim. He starts interfering, tickling her, stroking her under the knee. The chick starts feeling relaxed and gradually loses control not only over her thoughts, but also over her body. Her legs start moving apart, and a wet spot is growing on the panties."

She's actually reading Playboy, which would make for an interesting exam.