I didn't know this, but apparently Rockwell staged his artwork as photographs and worked from them. The differences between the original photograph and how the painting came out are fascinating.
Look at the couple in the photo. Her shoulders are slumped, she looks worried and hopeful. There's a sense that she's asking "please." He looks cold and impassive.
In the painting, it's almost a reversal. He looks chagrined. She looks sly. You can almost hear her thinking "there's more where that came from."