a fly in the ointment

Is an interesting idiom which is quite different to the German idioms.

This term must go back to medieval alchemists mixing strange medicines and finding dead insects in their concoctions.


Here are some other common uses of "fly" which you can feel free to use in English:

Must FLY! = Muss schon wieder los!

sparks FLY [coll.] = die Fetzen fliegen

to fly into a passion = in Wut geraten

I'd like to be a FLY on the wall. = Da würde ich gern Mäuschen spielen.

fly-by-night adj. = unverantwortlich; unverlässlich

He breaks a fly on the wheel. = Er schießt mit Kanonen auf Spatzen.