- Well, you see, Monsieur Inspector, a song is capable of many interpretations by a musician.
- By a detective, too. Though no doubt the detective is usually mistaken.

10 seconds sound clip from the Phantom of the Opera (1943) movie soundboard.

You can hear this line at 00:35:30.445 in the Blu-ray version of the movie.

Quote context

[...]

- Anatole, well, he's been helping me.

- Oh, Monsieur is very kind.

- Not at all, monsieur. I find it a pleasure.

- I'm Anatole Garron of the Opera.

- Oh, I'm so sorry. This is Inspector Daubert, of the Sûreté.

- I've heard of you, Monsieur Inspector. Your work must be exciting.

- Not so exciting as yours, monsieur. It doesn't lend itself to self-expression.

- I didn't recognize that delightful song you were singing, Christine. But as you know, I am no connoisseur of the opera.

- It's not from an opera, Raoul. It's a lullaby.

- A lullaby. It didn't seem very effective as a lullaby.

- Well, you see, Monsieur Inspector, a song is capable of many interpretations by a musician.

- By a detective, too. Though no doubt the detective is usually mistaken.

- I must see you alone, Christine. I'm here on business from the Sûreté.

- With me?

- What business could mademoiselle have with the Sûreté?

- What is it, Raoul? If you don't mind, I'd rather Anatole stay.

- Very well, Christine. You know Erique Claudin?

- Well, yes.

- How well?

- I knew him only as a violinist in the orchestra.

- I encountered him a few times in the foyer or on the stage or outside the Opera, but that's all.

[...]