Stop what you're doing and watch this. It's a video of sand. Sand skittering around on a vibrating plate, to be exact. But what happens when that sand skitters is amazing. Trust us – this is something you want to see.
What you're watching is the Chladni plate experiment, as performed by YouTube science-and-illusion wizard Brusspup (he can also coax water into a zig-zagging stream, and make Rubik's Cubes that aren't Rubik's Cubes).
When physicist Ernst Chladni performed this experiment in the 18th century, he did it with flour instead of sand, and made his metal plate vibrate with a violin bow instead of a tone generator, but the end result is the same: when the plate vibrates at a steady frequency, the particles on its surface arrange into a beautiful pattern.
The particles (sand, in this case) are arranging themselves along what are called "nodal lines" – narrow curves of motionless calm that criss-cross the otherwise vibrating surface. As the frequency changes, so does the distribution of these nodal lines, which becomes increasingly intricate at higher frequencies.
UPDATE: Brusspup has uploaded the full video of the experiment, with tones. WARNING: LOWER YOUR VOLUME. The audio in the clip could cause hearing damage.