Ferro

bring the magnet down. the puddle stands up to meet it.

a magnet over a puddle of ferrofluid: bring it close and the liquid rises in spikes, then leaps to it

Ferrofluid is oil full of tiny iron-oxide grains, so a magnet pulls on the liquid itself. Past a certain field the flat surface gives way and breaks into spikes, spaced by gravity and surface tension: a stronger field raises more of them over a wider patch, not fatter ones. Close enough, the pull beats gravity and the liquid jumps to the magnet.

Concepts: magnetism.

An interactive you play with one thumb, on Wundr.