Jimmy's in love with Kelly

In the scene where Grace Kelly put a note Raymond Burr's door and was able to escape the scene without getting caught, she returned to Jimmy Stewart's house. She started telling Jimmy and the maid of how thrilled she felt about doing that. At this point, the camera turns to Jimmy Stewart and he has a bright, happy face while he's looking right at Grace. Without any words needed to be given, the director is telling us how Jimmy is becoming very affectionate towards Kelly.

Yes instead of letting us think what we want about his face, the director wanted Jimmy's feelings to be clear to the audience so we wouldn't have to think for ourselves. The whole movie he wasn't sure about how he felt about her, he didn't really express the way he felt with his face, but as he looked at her after she did what he didn't think she,d ever have the guts to do, he finally realized and let us know what he really thinks of her.

I forgot to add that in the close up on his face as he smiled at her while she was telling her story there was enough time to think about his facial expression, so we can really have a grasp on his feelings. This was how average shot length was used