You can't mean that seriously.

2 seconds sound clip from the Isle of the Dead (1945) movie soundboard.

You can hear this line at 00:24:03.609 in the Blu-ray version of the movie.

Quote context

[...]

- That the Vorvolaka is an evil for which the gods punish us mortals.

- I suppose the next thing you know she'll be telling us that the Vorvolaka walks among us. What nonsense.

- The doctor is the doctor, and we'll do as he says.

- Certainly. But one might as well go out on the cliff, and build a votive fire to Hermes. Not that I believe in Hermes, either.

- You had better believe in the doctor. He's the only one who can save us.

- We'll make a wager. The doctor can use his science, I'll pray to Hermes. We'll see who dies and who is saved.

- You can't mean that seriously.

- I'll take your wager.

- You broke the doctor's first order. No contact.

- I'll break no more of his orders. Nor will you, or any of the others.

- But now that I find we are to remain here, I must insist that you stop.

- Your suspicions of her, your hints, your vague little threats, they all make Thea dreadfully unhappy.

[...]