What happens is the opposite of what was expected, or of what someone had planned, in a way that reveals something about the characters or about the world of the work.
In Madame Bovary
it was he, rather, who would have been taken for the virgin of the day before, while the bride did not let slip anything from which one could guess something
The one who seems the "virgin of the day before" is Charles, not the bride. The text reverses expectations: the husband is the one who seems innocent, while Emma "did not let slip anything," and this exchange of roles already sets the newlyweds apart.
Part I, Chapter 4, the narrator
They already knew each other far too well for those surprises of possession that multiply pleasure a hundredfold. Emma was as bored with Léon as he was tired of her. Emma now found in adultery all the insipidity of marriage
Part III, Chapter 6, the narrator
He has just received the Legion of Honor.
Part III, Chapter 11, the narrator
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