Surface Tension.
One of those physical properties that I can't quite wrap my neurons around.
http://en.wikipedia.org/wiki/Surface_tension.
Which takes us to Surface Energy. Related is Gibbs Free Energy, which I barely recall from Crystallography class decades ago.
As I understand it, when dealing with fluids in small, confined spaces, gravity is just another player. Besides the surface energy, there are chemical gradients as well, all part of a physically connected system attempting to equalize, to achieve entropy, creating interesting patterns along the way.
It's all quite beyond me, a simple prospector and map-maker, but it fills me with awe.
Oh, there's that guitar bit I like:
[youtube]rk9A_2xi-CA[/youtube]