- How could I have known about the secret passage?
- Easy. Yvette told you.

4 seconds sound clip from the Clue (1985) movie soundboard.

You can hear this line at 01:20:26.539 in the Blu-ray version of the movie.

Quote context

[...]

- Was it one of her clients? Or was it a jealous wife? Or an adulterous doctor?

- No. It was her employer, Miss Scarlet.

- That's a lie!

- Is it?

- You used her the way you always used her.

- You killed the motorist when we split up to search the house.

- How could I have known about the secret passage?

- Easy. Yvette told you.

- So when we split up again, you switched off the electricity. It was easy for you here on the ground floor.

- Then, in the dark, you got the lead pipe, and the rope, strangled Yvette, ran to the library, killed the cop...

- Picked up the gun where Yvette dropped it, opened the front door, recognized the singing telegram from her photograph, and shot her.

(Gunshot) (2)

[...]