It is also revealed what a Parselmouth is: someone who can speak to snakes.
We have known Harry can do that -- because a boa in the zoo spoke to him in Philosopher's Stone. But we realise that it is not a common -- or welcome -- gift for even wizards. Many in the school think Harry is Salazar Slytherin's heir -- he was a Parselmouth and Voldemort, being his descendant, also was one -- who has opened the Chamber of Secrets.
Harry, Ron and Hermione set about investigating what the Chamber is, where it is, who opened it and why. But Hermione is Petrified too.
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