- You don't know that.
- I do know that, actually.
- No, you don't.
- No, actually, I do.
- No, you don't.

7 seconds sound clip from the How to Train Your Dragon movie soundboard.

You can hear this line at 00:10:23 in the Blu-ray version of the movie.

Quote context

[...]

- And, while I'm busy, Hiccup can cover the stall.

- Molten steel, razor-sharp blades, lots of time to himself. What could possibly go wrong?

- What am I going to do with him, Gobber?

- Put him in training in the others.

- No, I'm serious.

- So am I.

- He'd be killed before you let the first dragon out of its cage.

- You don't know that.

- I do know that, actually.

- No, you don't.

- No, actually, I do.

- No, you don't.

- Listen, you know what he's like. From the time he could crawl, he's been different.

- He doesn't listen. He has the attention span of a sparrow.

- I take him fishing and he goes hunting for trolls!

- Trolls exist. They steal your socks. But only the left ones. What's with that?

[...]