As the siblings huddle together for warmth, their bodies betray them. The brother's cock stiffens, pressing against his sister's thigh. She gasps, her pussy clenching in response. Their eyes meet, filled with a mix of fear, desire, and guilt. They know they shouldn't, but the taboo nature of their act only heightens their arousal. She tentatively reaches out, her hand wrapping around his cock. He bucks into her touch, their breaths coming in short gasps. They're past the point of no return, their bodies demanding release, their minds be damned.