Eavesdropping and watching

Just because I titled this post "Eavesdropping and watching", don't think I spend time peering into windows or pressing my ear to doors. I just love people watching and part of that involves listening to them.
Walking through the aisles of Gerrity's yesterday, I kept bumping into a young woman with two girls, so I made a number of observations about them based on the way they moved and snippets of their conversation.The woman, the girls' mother I presume, walked quickly and spoke to the girls about the tasks on hand: pick some apples you'd like, oatmeal or cereal this week? etc. The older girl, about 13 I figure, showed the classic "I'm so embarrassed to be seen with these people" attitude by her clipped answers, her shuffling feet, and her downward gaze. When her mother's back was turned, she grabbed a box of chocolate granola bars and silently tucked it into the basket. The younger girl, probably about 10 years old, was chock full of energy and entertained herself (and me). Without prompting, she grabbed one of those premade flower bouquets. "Oh, thank you," she said to no one in particular. She curtsied. "I'm honored." Her mother rolled her eyes and smiled. Her sister moved away.
In the dairy aisle, I caught up to the younger girl choosing yogurt. She lifted one and said, "If this is Greek yogurt, how come I can read the label? I don't know Greek." and "Ooh, la la. Zis yogurt iz French." You get the idea. Her mother stood nearby, smiling and apparently enjoying this kid's antics. Her sister hid among the baked goods.
I guess what I'm saying is I watch people and listen to them because I learn a lot that way. Being a student of human behavior comes in handy when I'm trying to write realistic dialogue or show a character's traits and emotional state.