You're quite mistaken, Baron.
4 seconds sound clip from the Frankenstein (1931) movie soundboard.
You can hear this line at 00:25:48 in the Blu-ray version of the movie.
Quote context
[...]
- He said he would get in touch with you soon.
- Don't worry about him, Baron. He'll be home in a few days.
- You two have it all arranged, haven't you?
- You think I'm an idiot, don't you? But I'm not.
- You're quite mistaken, Baron.
- What's the matter with my son? What's he doing?
- He's completing his experiments, that's all.
- Oh, Baron, you don't understand.
[...]