The White fluid on the left is a non Newtonian fluid, the black fluid (right) is a ferromagnetic fluid (ferrofluid).
A non-Newtonian fluid is a fluid whose flow properties differ in any way from those of Newtonian fluids. Most commonly the viscosity (resistance to deformation or other forces) of non-Newtonian fluids is not independent of shear rate or shear rate history.
Ferrofluids are colloidal liquids made of nanoscale ferromagnetic, or ferrimagnetic, particles suspended in a carrier fluid (usually an organic solvent or water).
Each tiny particle is thoroughly coated with a surfactant to inhibit clumping. Large ferromagnetic particles can be ripped out of the homogeneous colloidal mixture, forming a separate clump of magnetic dust when exposed to strong magnetic fields.
I think both are pretty cool.

^ A ferrofluid on glass, with a magnet underneath.

The White fluid on the left is a non Newtonian fluid, the black fluid (right) is a ferromagnetic fluid (ferrofluid).

A non-Newtonian fluid is a fluid whose flow properties differ in any way from those of Newtonian fluids. Most commonly the viscosity (resistance to deformation or other forces) of non-Newtonian fluids is not independent of shear rate or shear rate history.

Ferrofluids are colloidal liquids made of nanoscale ferromagnetic, or ferrimagnetic, particles suspended in a carrier fluid (usually an organic solvent or water).

Each tiny particle is thoroughly coated with a surfactant to inhibit clumping. Large ferromagnetic particles can be ripped out of the homogeneous colloidal mixture, forming a separate clump of magnetic dust when exposed to strong magnetic fields.

I think both are pretty cool.

Ferrofluid on glass, with a magnet underneath.

^ A ferrofluid on glass, with a magnet underneath.