You sound as if you don't believe me.
3 seconds sound clip from the The Roaring Twenties (1939) movie soundboard.
You can hear this line at 00:38:52 in the DVD version of the movie.
Quote context
[...]
- You see, I spend all my spare time studying.
- Someday I'll be a musical-comedy star.
- And you're dancing in the chorus to get enough money to pay for your music lessons.
- You'd rather not, but a girl has to live somehow, doesn't she?
- You sound as if you don't believe me.
- I do, I certainly do. Why wouldn't I?
- I'm so tired I can hardly get up.
[...]