An ellipsis of "now that you have come to mention it"
- (idiomatic) What you just said reminds me of something; Used to justify a change of subject or a kind of statement that needs some kind of license.
- "What do you think of the banking reforms?" / "Come to mention it, I've got to get to the bank before it closes today.
- "Did you see that hat he was wearing?" / "Come to mention it, he always wears funny clothes."