Water.

At least that's the conclusion of traffic engineers. They don't say it that way. Their language is more like, "traffic flow is most closely modeled by the equations of hydrodynamics." but they mean the same thing; people in cars behave like water flowing through a pipe.

Turbulence explains the slowdown at onramps, the venturi effect explains what happens when they close off lanes for road work and fluid waves are responsible for the molasses stop and go of rush hour traffic.

We can take this one of two ways: either we get as dumb as water molecules when we get into our cars and onto the road (there is a lot to be said for this hypothesis, remember that idiot who cut you off the other day?), or water molecules are a lot smarter than we realize.

Think of the conversations in the plumbing, "Get out of the way you ionized bum!"

"I just hate it when those bruiser proteins come hauling down the pipe and blow everybody else out of the way."

This could revolutionize Quantum Mechanics; what we take as Brownian or Quantum randomness might be conscious decision making at the molecular level, "I just didn't feel like going through both slits today; it's been a long day, I had a fight with my wife, you know...."

Before you start worrying about yet one more endangered species and the EPA telling us what and when and where and how we can drink, the vast majority of water molecules outlive humans. I don't know how well that argument would go over with the bureaucrats, however; they're liable to worry about the quality of those poor water molecules' lives.

The human body is 98% water. Hmmm, maybe we're conscious only as a result of the water molecules in our body.... Naw, that would be ridiculous.