What the scribble is doing

There are no soft edges in the scribble drawings. A hand is not lighter on one side than the other. It is either dense with line or it is not.

So most of it comes down to speed. Slow scribble turns into hatching and the drawing dies on the spot. Fast scribble piles up into something that holds together from across a room and comes apart when you walk up to it.

The one with the five hands shows it plainly. Each hand keeps to a single colour, so the only thing separating them is how tightly the line is packed.