- Oh. You don't believe that, do you?
- Mm-mmm.

6 seconds sound clip from the Miracle on 34th Street (1947) movie soundboard.

You can hear this line at 00:20:09 in the Blu-ray version of the movie.

Quote context

[...]

- I thought as long as we're in the store, you might as well say hello to Santa Claus.

- Why?

- Well, because when you talk to him, you might feel differently about him.

- Good-bye, Elmer. Be a good boy now.

- Merry Christmas!

- Well, young lady, what's your name?

- Susan Walker. What's yours?

- Mine? Kris Kringle. I'm Santa Claus.

- Oh. You don't believe that, do you?

- Mm-mmm.

- You see, my mother's Mrs. Walker, the lady who hired you.

- But I must say, you're the best-looking one I've ever seen.

- Really?

- Your beard doesn't have one of those things that goes over your ears.

- That's because it's real, just like I'm really Santa Claus. Oh, go ahead. Pull it.

[...]