Digging up knobbed puzzle pieces

I am always on the lookout for ways to re-use materials and trying to make further use of a knobbed puzzle the other day I set up a really simple activity that kept M busy for a while. These puzzles are the kind of material that after a few uses become old hat. I fear that is one of the disadvantage of most non open-ended materials. But well, with a bit of imagination we can reuse them!
For this activity you only need the wooden already mastered puzzle, a tray, and flour, salt or corn-starch. I covered the pieces with starch and presented it next to the base of the puzzle. I added a thick paintbrush as an invitation to uncover the "treasure".
M eagerly took the brush and dug up the pieces. She was quite excited to see what was buried there!