Colored droplets in corn syrup can be mixed and then unmixed by reversing the mixing motion thanks to a phenomenon called Stokes flow or creeping flow, similar to how lava flows happen. It almost looks as if the video is simply reversed. Via University of New Mexico:
This apparatus allows for the visual examination of a fluid undergoing laminar flow. Initially, within the apparatus, various colored droplets are suspended in a fluid (corn syrup) and all are in a state of equilibrium where the different fluids are distinctly separated. When the apparatus is rotated the fluids revolve in a controlled manner and the droplets seem to become completely intermixed yet still divided from the outer fluid. After several rotations the apparatus is then operated in the reverse direction. Since the Reynolds number within this apparatus is less then one, an almost complete reversal of the previous laminar flow is undertaken. The result is that after the same amount of rotations in the opposite direction, the droplets return to their initial, distinctly separated, forms.
Image: UNM Physics and Astronomy
