A vortex is a physics phenomenon that occurs when a gas or a liquid moves in circles. At the center is a vortex line that the matter swirls around. They are formed when there is a difference in the velocity of what surrounds the line. Hurricanes, tornadoes and air moving over a plane wing are examples of vortices. In this video a plate is moved through the still water of a pool creating twin vortices that stay together as they move across the pool. How do they do that?
The trick is that the plate is round. As opposed to a canoe paddle or cold and warm air crossing and creating a tornado, the rounded bottom of the plate creates a semi circular vortex line instead of a straight line. It's this curved line that connects the two vortices (formed on either side of the plate) and keeps them moving together. The half ring vortex line is a unique event in physics and adding the food coloring shows that it's capable of moving matter.