About this scene
Long-distance bus, leather seats, half full. She's wearing a clean wool coat, expensive handbag on the seat beside her, paperback open. He sits one row back and across. The flash happens during a tunnel section when the cabin lights dim. She doesn't move for almost a minute, then her hand goes under her coat and stays there. By the time the cabin lights come back up her face is flushed, and ten minutes later she's in his row giving head with her coat draped over both their laps.
What to watch for
The coat is the cover and the prop. Watch how it migrates. Starts buttoned, becomes unbuttoned, slips down her shoulder, and ends up across both their laps as the visual shield. The handbag stays on her seat the whole time, untouched. That's a deliberate choice. She's signalling she'll be back in her own seat shortly. The PA announces the next stop two minutes before they finish and she keeps going.