Here’s a cool aspect of fluid dynamics that you might not have thought of before: When a shape is pushed into the water, it creates a space in its wake. As the space collapses, the shape inverts itself.
This is cool! When a shape like a star is pushed into a fluid, the “points” on the star collapse inwards quickly and become the hollows of the star, and the hollows collapse slowly and become points.
This is cooler. When the curves get sharp enough, as they do with the “star” towards the end of the video, the inverted shape re-inverts itself, and the original star “reemerges.”