[Petronski]

I posted four pictures: a box of rocks, a bag of sand, Huckster, and a sack of gravel.

[Cletus.D.Yokel]

Dumber than a box of rocks, the IQ of a sack of gravel...not familiar with the standard “bag of sand” allusion.

[eastsider]

I think the photo in the upper left is a tofu mold; the pebbles on top press the water out.