- I can see you know nothing about filing handcuffs.
- Hmm. I'm sure you do.

6 seconds sound clip from the The 39 Steps (1937) classic radio play.

You can hear this line at 00:34:05 in the radio play.

Quote context

[...]

- What a bloodthirsty creature you are. Haven't you any pity?

- No.

- Ow! What are you up to now?

- I'm merely trying to file the handcuffs.

- Well, don't jab me in the wrist that way. I don't like it.

- I'm sorry.

- You're going about it in a very amateurish fashion anyway.

- I can see you know nothing about filing handcuffs.

- Hmm. I'm sure you do.

- Tell me, how did you start being a criminal?

- So you want the story of my life. It's really very interesting.

- Oh, I'm sure it is.

- I was born a poor orphan boy. From the beginning, I hadn't a chance.

- Ouch!

- I'm sorry, it slipped.

- Accidentally?

- Accidentally. Go on, please.

[...]