Harry Potter and the Chamber of Secrets2002

[Harry runs into the Gryffindor common room. Ron and Hermione follow him.]

Ron:
[Stops Harry] You're a Parselmouth? Why didn't you tell us?

Harry:
[Confused] I'm a what?

Hermione:
You can talk to snakes.

Harry:
I know. I mean, I accidentally set a python on my cousin Dudley at the zoo once. Once. But so what? I bet loads of people here can do it.

Hermione:
No, they can't. It's not a very common gift, Harry. This is bad.

Harry:
What's bad? If I hadn't told that snake not to attack Justin–

Ron:
That's what you said to it!

Harry:
You were there. You heard me.

Ron:
I heard you speaking Parseltongue. Snake language.

Harry:
[Surprised] I spoke a different language?

[Ron nods.]

Harry:
But I didn't realize– How can I speak a language without knowing I can?

Hermione:
I don't know, Harry, but it sounded like you were egging the snake on or something. Harry, listen to me. There's a reason the symbol of Slytherin house is a serpent. Salazar Slytherin was a Parselmouth. He could talk to snakes too.

Ron:
Exactly. Now the whole school's gonna think you're his great-great-great grandson or something.

Harry:
But I'm not! I can't be.

Hermione:
He lived a thousand years ago. For all we know, you could be.