Ever played "shadowgrams"?
It's surprising the variety of shapes you can create with your hands.
The problem is that all too often hands are too big, and you can't reach out into the center of the print.
That's why we tape something on the end of a stick or wire to put a shadow over a hot spot out in the middle of the print.
As others have said, tilting and/or rotating the dodger at various heigths above the easel can create a wide variety of shapes and shadow densities.
Here's a brocure I include with my 8-piece dodger set that gets a lot of favorable comments: