I held the mirror up to the tank again, to show my kids how Perry flares. He made a move I hadn't seen before- came up very close to the mirror image, and slowly tipped his body horizontal, as if lying down in the water, with a twisting threatening motion. It was very curious looking, very deliberate, and my daughter was amazed. When I pulled the mirror back he would energetically dash up and down the front of the tank looking for the 'other fish'.
So fast to move, it was hard to get a decent photo. Here's my best