Gosh, Pat, I have been collecting these expressions for as long as I have lived in France! Could spend hours talking about them so I will just tell you my most recent.
donner la langue au chat
I don't have a true translation but I have my own idea about it which may or may not be correct. I use it in the sense of "it's in the lap of the gods" which I am sure would not mean anything to a French person! To put it another way, it's expressing an inability to explain something and so "I have given up trying to find a solution to the problem".
Perhaps someone can explain it better, svp?
Apprendre une langue, c'est faire un voyage différent chaque jour.
from Fle pour les curieux