What stays with him is how fast she can put the sweetness back on. One second there is the slow look, the quiet after the sentence, the detail left exactly where his eyes found it.
Then someone walks up.
She is soft again. Polite voice, easy laugh, harmless answer. Nothing for the newcomer to notice. Nothing strange enough to mention later.
That switch ruins the old version for him. The gentle smile does not look simple after that. It looks controlled. She can pass through a room as the nice one, then tilt one second toward him and turn it off before anyone else catches up.