My clown loaches having a barny, don't know why. They did it for about four minutes then went their separate ways, I think the bigger one won. The secon half is clearer when I moved closer.
This is the dance they do when they are fighting for alpha in the tank. Mine just did this today as a matter of fact! Notice how one is grayer than the other? When one colors up again it means he is tanking the loss and the other one is the dominant one. Here is a link to another post on this