For the young subject and her object of interesting, learning more about this new discovery is their sole focus.
The background in this painting is not a mere wash of colour. Instead, the artist has added more details to interest those who have taken the time to look at his painitng. Two men can be seen in the background. One of the fishermen seems to have nets slung over his should and is slightly slouched. They may be discussing the day's catch or the best time to launch out to sea.
The sun is relatively high in the sky. At this time, the boat and the commercial activities of their day may be their chief concern. They need to provide for their families. For the young girl, it is entirely different. She is caught up in a quiet place, playing with her crab. She is not worried as they may be about whether sales will go well or they will catch enough fish on that day or the next. She just wants to see how the crab will respond to the stick that she is using to poke it.
It seems that Bouguereau has gone the extra mile to create a context for the girl and her crab. In a minute, it seems she may lose her new playmate. It may either become a part of her dinner or be sent back to sea. The viewer is left to wonder if the men are related to her. She may have come to the seaside to spend the day with her father or an older brother.
This use of context makes the painting more interesting. It gives the viewer a story to think about. The artist has focused on the crab and the girl by using sand to partially block the other people in the painting from view. However, they remain in the background to remind those looking on that she is not unsupervised. Dressed in casual clothing, she is a part of a bigger story.