I was just wondering if there is a particular meaning for this expression.
I read this in a book, and it seemed like it was a warning of some sort, but I can't be certain.
Thanks in advance!
Context: (as far as I could tell)
There was a man carrying a baby while running in a dark alley. There was a crow perched on a roof cawing "Au plus dru! Au plus dru!" And then later on, when the baby grows older, she sees "au plus dru" at the front of a hotel on the stone of the pediment.