Now You Mention It Meaning

(idiomatic) (Used to precede another comment about something just mentioned)

Example: 1894, Rudyard Kipling, The Jungle Book
  I--I--I have fought a little, but not in that climbing way or that running way.
  Now you mention it," said Billy, "you don't look as though you were made for climbing or running--much. Well, how was it, old Hay-bales?
1922, James Joyce, Ulysses Episode 16
  --Everybody gets their own ration of luck, they say. Now you mention it his face was familiar to me. But, leaving that for the moment, how much did you part with, he queried, if I am not too inquisitive?