- Something introduced into the blood streams that caused their death.
- What could it be?
- I don't know. That's what I have to find out.

10 seconds sound clip from the Murders in the Rue Morgue (1932) movie soundboard.

You can hear this line at 00:28:30.173 in the Blu-ray version of the movie.

Quote context

[...]

- After the carnival last night, I performed an autopsy. The victim didn't die of drowning. There was no water in her lungs.

- Oh, so that's what you were up to. I thought you were with Camille.

- Of what did the victim die?

- Here it is again.

- What?

- The same foreign substance in the blood of each victim.

- Look. All three died from the same cause. Some strange poison perhaps.

- Something introduced into the blood streams that caused their death.

- What could it be?

- I don't know. That's what I have to find out.

- Oh, Pierre, you must pull yourself together. Why, you're becoming fanatical. Look at yourself in the mirror. Your eyes are getting glassy. Just like that old charlatan's.

- Dr. Mirakle, eh? What did you make of him?

- Oh, he's a faker.

- Did you pay attention to what he said?

- You mean about us being the product of evolution?

- Yes. Has it occurred to you that he might be right?

[...]