> In the US eggs at the supermarket are very clean. In Europe, it's forbidden to clean the eggs in any way. Often enough, you will have feathers and feces on eggs bought in the supermarket.

Cleaning them removes a natural antibacterial layer that protects the eggs, which is why the US has to refridgerate theirs and Europe leaves them out at room temp. http://www.npr.org/sections/thesalt/2014/09/11/336330502/why...