The energy of casting something about randomly. If in the present or future, it is a thing: straw. If it is in the past, it remains an action: strewn. This action differs from “scatter”, which is the sound of something being strewn on a hard surface. Seeds from grass are scattered, but the grass is strewn to become straw. Straw is never singular. It is a group. Before being strewn, though, straw is a series of stalks. Of them you can have one, but if you strew it it never becomes straw. At best, it is a stalk of straw.
Strewn Grass and Scattered Seed in a Winter Thaw