At 30,000 feet, sibling hormones take over. In the tiny lavatory, they stand, bodies pressed together, hands exploring. She unzips him, strokes his hardening cock, while he lifts her skirt, fingers her wet slit. She turns, bends over the sink, and he enters her from behind, fucking her hard and fast as they both struggle to stay quiet. Their reflections in the mirror, eyes locked, only add to their taboo excitement.