dude the legendary dan Egan eyebrow raise in Nevada was improvised I LOVE MY TRASH CHILDREN
Actors tend to have good instincts for this stuff, so I’m not surprised – it really is the eyebrow…wiggle, I guess is the word for it, that MAKES the scene (and Amy’s response to it, of course). It’s creates a sense of…complicity, I guess, that Dan is as aware as Amy of what exactly is going on between them, and is happy about it. (As opposed to the scene in Tehran, where he implies that and then leaves her to twist in the wind – he is such a terrible, awful person).
But one thing that has been absolutely drummer into me as a playwright is not to ‘script’ the actor to death. It’s different for theatre than film, of course, but I think it’d be fairly uncommon for an actor’s actions to be scripted to that level of detail. You’ll see it from time to time – if a particular action is REALLY crucial to the plot – but as a rule of thumb, it’s always better to script the reaction (scared / sad / frustrated / whatever) and leave it to the actor to work out how they should physically convey that feeling.