Here's a science experiment you can pretty much duplicate at home:
Physicists at the University of Chicago essentially dropped a marble into loosely packed sand, producing a jet of sand grains that briefly behaves like a special type of dense fluid.
They describe it as a novel state of matter.
"We're discovering a new type of fluid state that seems to exist in this combination of gas—air in this case—and a dense arrangement of particles," said lead researcher Heinrich Jaeger. "It's just a most amazing phenomenon.