Every country has it's own expressions, and to the French we British are crazy! Here's a few examples of how different our minds work ...
English : Raining Cats & Dogs - French : Raining Ropes
English : As Easy as Falling off a Log - French : As Easy as Fingers in your Nose
English : Filthy as a Pig - French : Filthy as a Comb
English : Smoke like a Chimney -French : Smoke like a Fireman
English : Bull in a China Shop - French : Elephant in a China Shop
English : Subtle as a Sledgehammer - French : As Fine as Coarse Salt