- What makes you so sure that I'll marry you?
- Because you promised. And because of this.

8 seconds sound clip from the The Curse of Frankenstein movie soundboard.

You can hear this line at 00:27:58.800 in the Blu-ray version of the movie.

Quote context

[...]

- I'm sorry. Perhaps I shouldn't have spoken to you like this.

- I'm sorry, too. I lost my temper. Please, forgive me.

- Really, just because it was arranged years ago that's no reason for my not marrying Victor. It has always been my dearest wish. His, too.

- Victor...

- How many times have I told you?

- Baron, then. Herr Baron.

- That's better.

- How much longer is this to go on? Meeting like this in dark corridors. Making love in secret. When are you going to marry me?

- What makes you so sure that I'll marry you?

- Because you promised. And because of this.

- Herr Baron Victor, this woman, what is she doing here?

- Are you jealous?

- No. Yes. Yes, I am jealous.

- She's not your mistress? If I thought she was...

- On the contrary. She's to be your mistress.

- It will be your duty to serve my cousin Elizabeth. And see to her every need as thoroughly as you have mine. But in a different way of course. Of course.

[...]