The ball at the château of Vaubyessard, the home of a marquis, in Part I, is the night Emma sees the world of the nobility up close and, not knowing how to waltz, dances guided by a viscount. The ball works like a poison, because it shows her, for one night, the life she will spend the rest of the book trying to repeat.
The marks of the ball run through the story. On arriving in Yonville, Emma counts Vaubyessard among the places that opened a new phase of her life. Their daughter is named Berthe because Emma recalls hearing "the marquise, at the Vaubyessard château, call a young woman Berthe." When Léon leaves, she feels the same melancholy as "on the return from Vaubyessard." At the agricultural show, the scent of Rodolphe's hair brings back to her "the Viscount, with whom she had waltzed at Vaubyessard." And among the gifts she gives Rodolphe is a cigar case like the viscount's, which Charles had found on the road and which Emma kept.
The viscount returns almost at the end. In Rouen, already ruined and after Léon's empty promise, Emma thinks she sees him pass in a tilbury, "But it was the Viscount!" and soon thinks she was mistaken, because she knew nothing about him. The text closes the moment with "Everything, inside her and out, was abandoning her."
The ball does not seduce Emma, it poisons her. If the problem were only the poverty of Tostes, that night should have satisfied her, since it gave her the world she lacked; instead, it sharpened her hunger. From it comes the pattern of excitement followed by a greater boredom, which repeats itself with each lover.