Separation

Did I went dumb from night to day, I simply don't get what you can't understand =X

Let me try to use Your analogy of fishes in water.. If You watch a shoal, or a school (same fish species and swimming with much more synchronicity..), don't the fish sometimes bump into each other? Do they fuse together?

Don't overthink it ;)

Floating Rocks

I think You're forgetting the current/movement of the medium, like, if You put some grains of sand( higher density than water in this case ) in water and stir it, won't the sand go with the flow?

Density

Physics do behave slightly different between orders of dimension, micro, macro, nano..

Static

If they're static there is no movement, so You answer Your own question, if You've paid attention to words meaning =Þ, and skin actually allows water and waste to get out, it's called sweat.. Sort of different compositions but I think I see what You're saying with the comparison of blood and bread, although one is animal ant the other don't =)

Take care ;)