What is the body and who are the characters of the story "A Piece of String"?
If you are referring to the group of people who trod along, on their way to the market, that would be the body:
The whole body bent forward at each movement of their long twisted legs; deformed by their hard work, by the weight on the plow which, at the same time, raised the left shoulder and swerved the figure, by the reaping of the wheat which made the knees spread to make a firm "purchase," by all the slow and painful labors of the country. Their blouses, blue, "stiff-starched," shining as if varnished, ornamented with a little design in white at the neck and wrists, puffed about their bony bodies, seemed like balloons ready to carry them off. From each of them two feet protruded.
As for the main characters, "Maître Hauchecome of Breaute had just arrived at Goderville, and he was directing his steps toward the public square when he perceived upon the ground a little piece of string."
Maitre Hauchecome is the first main character to be introduced. He is quite frugile; therefore, he picks up a piece of string to save for a possible need later on in life. When he picks up the piece of string, "he noticed Maître Malandain, the harness maker, on the threshold of his door, looking at him. They had heretofore had business together on the subject of a halter, and they were on bad terms, both being good haters."
Maitre Malandain has been observing Maitre Hauchecome. He noticed when he picked up the piece of string. Of course, he is not certain as to what Maitre Hauchecome has actually picked up. When a wallet is later missing, Maitre Malandain accuses Maitre Hauchecome of scooping up someone's wallet. Then the story begins to take shape.
Later, the wallet is found and returned to its rightful owner. Maitre Hauchecome is cleared from the accusation that he had picked up someone else's wallet. Of course, it is too late. The damage has been done. Too many people think that Maitre Hauchecome has had some part in the missing wallet.