Hint: The above video still shows a simulated example of the phenomenon they share.
When you place a dense layer of fluid atop a less dense layer of fluid, it results in what physicists call a Rayleigh-Taylor instability. You can observe this effect in everything from salad dressing to lava lamps to evolving supernovae. Two-dimensional numerical simulations of the RT instability, like the one featured here, are used to study its properties.
https://gizmodo.com/a-gorgeous-demonstration-of-rayleigh-taylor-instability-5969206
https://gizmodo.com/researchers-create-two-different-kinds-of-lava-lamp-5976317
The waviness of the initial interface provides a perturbation—a small disturbance—which grows in time. The two fluids spiral into one another in a fractal-like mushroom pattern. The continued motion of the dense fluid downward and the lighter fluid upward mixes the entire volume toward a uniform equilibrium.
