The magic mill. Traditional tale from Norway.

The secret of why the sea is salty
An intrepid sea captain landed in a port on the Norwegian coast to do business. There a merchant sold him some huge blocks of salt. The captain loaded them into the hold of his ship and set sail for new destinations. Along the way, a storm broke out that made him stop on an icy islet.

There, to the amazement of the sailors and the captain himself, an old wizard was grinding huge blocks of stone with a strange machine, just by saying: "Grind that grinds you."

The entire crew hid behind some rocks and waited for the magician to finish his ceremony to… steal such an incredible apparatus. In the dead of night, they loaded the machine onto the ship and set sail without being seen. The captain was so happy that he kept saying the magic words so that the machine would not stop grinding the blocks of salt.

But after several hours the ship's hold and deck were filled with salt, so that there was no room. And as much as the captain invented words to stop the infernal apparatus, it kept grinding you grinding. Until they had to abandon ship and let it sink into the deep sea, where it continues to grind salt.