Here a picture: https://ibb.co/k28CcTYS

We keep finding soil, a good amount, it's like dry clay, under our pillows. 3 nights in a row under mine, 1 night (tonighr) under my husband's pillow. The bed is made every morning and we use 3 pillows one on top of each other. When we go to bed everything is still in place. Just after a while we notice the small pile/pieces of soil under our pillows.

We have a cat but he is super small and calm, he wouldn't even be able to lift the pillows. And he stay mostly in my son's bedroom, and nothing similar happened in his room. No, it's impossible that this is my son doing it, he never gets anywhere near our room.

My husband has a theory that wasps are bringing this soil during the day and we just don't see them.. to me this doesn't make any sense.

Is there anyone who have heard something similar? What could it be?