A Phantom of the Opera question

Cafe Society
1

I’ve been reading Gaston Leroux’s Phantom of the Opera and am stumped by a passage that I’m guessing is a tramslation of a French pun. The Persian, an acquittance of Eric, had previously made Eric promise to forgo any more murders. When reminded of the promise Eric says: “Oaths are made to catch gulls with”.
Is that a pun or a maybe a punch line for an ancient joke?
BTW, PotO is a pretty fun read.

2

Perhaps “gull” in the meaning of “gullible”, someone who’s easily fooled?

3

Yes, Shakespeare used “gull” to mean “fool”, more or less: SCENE VI. The English camp in Picardy.

4

[moderating]
Moved from GQ to Cafe Society, where book-related questions tend to get good answers.
[/moderating]

5

But would the pun work in French?

6

It’s not a pun, it’s just slang. I have no idea how the line was rendered in French, though.

7

“Gulls” isn’t in the French. The original French text reads

which translates to “Oaths are made to catch simpletons”. Whoever translated it to English used the gulls thing, so I’m guessing it’s not meant to be a pun.