The siblings' game of chicken escalates as she leans in, her generous cleavage pressing against his arm. He swallows hard, his cock twitching in his pants. She notices, a smug smile playing on her lips. "You're hard, aren't you?" she whispers, her breath hot on his ear. He nods, unable to speak. She leans back, her eyes never leaving his, and slowly, tantalizingly, she begins to rub her boobs, her nipples hardening under her top. He watches, entranced, as she offers him a show he'll never forget.