Here is a line from near the beginning and another from near the end of a scene (this is from Middlemarch, btw):
Beginning: Rosamond colored deeply. "Have you not asked papa for money?" she said, as soon as she could speak.
Ending: "Are we to go without spoons and forks then?" said Rosamond, whose very lips seemed to get thinner with the thinness of her utterance. She was determined to make no further resistance or suggestions.
What's changed? Scenes are about change, about what effect the events and choices have on the characters. The change event here is that Lydgate (the husband) has confessed to Rosamond that they are in financial difficulties (because of his professional choices and her extravagance) and must cut back, even to the point of returning the silverware they had recently bought (hence her comment about spoons and forks).
But the effect of this revelation is complex. Rosamond makes what she thinks of as helpful suggestions (ask Papa for help, negotiate with the creditors, move to cheaper area), and Lydgate kindly deflects each one, until she finally gives up and decides just to be stony-silent with him. She realizes that he doesn't respect her, and even thinks that if she'd known this before, she wouldn't have married him. So she starts out feeling all wifely and loving, and ends up cold and alienated.
So notice how the simple physical description shows the change. It doesn't show it directly, but notice what changes. Early in the scene, she "colored deeply"-- that is, she blushes. That is a "young" physical manifestation, and it emphasizes her as almost childlike (which is how he is going to treat her).
Then, in the end of the scene, her lips "thin". That's an "old" physical manifestation, and shows how, as a result of the events of the scene, she is no longer naive and childlike, but older, wiser, and more bitter.
That's just an example of how you can use minor physical description to set up a "before" and then show an "after" in the scene.
Can you think of other examples? What about a scene you're working with? What changes? How can you show this?
I've got a scene where two sort-of friends are alone for perhaps the first time, having dinner. They start out as somewhat alien to each other, and end up kissing in the end. I have the "end" physical manifestation, of course, that they kiss. Maybe to emphasize the change, I can show them physically -not- together in the beginning, like she deliberately takes a seat across from him rather than next to him, because they are, of course, not lovers yet. :)