Why, you've got to believe it. What can I do? What will do to prove to you I'm not lying?
9 seconds sound clip from the Anna Christie (1930) movie soundboard.
You can hear this line at 01:25:20 in the DVD version of the movie.
Quote context
[...]
- Oh, what's the use? What's the use of me talking? What's the use of anything?
- Oh, sure, Anna, if I could only be believing you, now.
- Why, you've got to believe it. What can I do? What will do to prove to you I'm not lying?
- Anna, would you...? Would you be willing to swear an oath, a terrible, fearful oath?
- Oh, sure, I will, Matt, on anything.
[...]