About this scene
Big-box store personal-care aisle, weekday, light traffic. She's shopping with her boyfriend. He's standing right next to her looking at a different shelf. The flash comes from the far end of the aisle. Her face still does the thing. She catches herself in two seconds, resets, and pretends to keep shopping. The boyfriend never looks up. She glances back down the aisle one more time before they leave.
What to watch for
The boyfriend obliviousness is the comedic frame. He is two feet from her, completely unaware. Watch her hand on the product she's holding. It tightens. Her shoulders pull in slightly. The reset is fast but not perfect. She slows her shopping pace measurably for the next thirty seconds and she puts back two items she had been considering buying. The second glance back down the aisle is the involuntary one. She is checking if he's still there.