I had a little time one day and decided to play around to try and capture the idea of slippery light - light that would reveal intention rather than detail - light that wouldn't let the viewer be comfortable. (bigger)
The closest I got to achieving this that day was to use a much larger aperture with a slower shutter followed by a very low power output flash in rear sync. (bigger)
One thing I learned was that if the external flash is triggered optically (by CLS) rather than by a cable, the preflashes occur with a sufficient delay that the birds will respond and be in motion when the shutter opens (could be a good thing if the focus was set to expect this - not so good here). (bigger)
So while I didn't figure out how to make slippery light yet, I learned a few things that have started me down the path to figuring it out (I really need to pull out my triggers to do the next set of experiments).