Today, I experimented with the Dodge and Burn tool. The point was to create shades and ripples.
In the end I figured out a new technique that shows interesting effects:

I started with this:

Then I selected the burned tool and played around a little with the brush settings. I created some deep shadows and then added a little light with the dodge tool.

After a few tens of minutes the result was this:

First thing that comes into mind is muscles, tendons, organic material. After a few retouches I called it a finished experiment:

Maybe I’ll make a tutorial named “How to create organic material in Photoshop CS5″