A brother and sister, always close but never crossing boundaries, find themselves in a sudden, intense moment of intimacy. She playfully asks, "What if we played with your dick?" He swallows hard, his mind racing, but agrees. She guides him to sit, then kneels between his legs, her eyes locked onto his. She takes his growing erection in her hand, feeling its heat, before leaning in to take it into her mouth. He gasps, his hands instinctively going to her hair, as they begin to explore the taboo, their hearts pounding with excitement and fear.