…when you find bits of limescale in your tea but are too lazy to descale your kettle
also, I learned a new interesting word today: limescale
the "German has a word for everything" myth is a myth, English has a word for… limescale
in German it's just a super ambiguous generic word that usually means the mineral/related stone/whatever, not the thing that you find in your kettle
…wikipedia informs me that there is a German word for this as well, but I refuse to accept it because it do not like it and am not planning to use it, ever
