For some of my marine rays, I used to make frozen cubes of fish juice and water. Outside of a normal feeding time, I would toss in a couple of blocks and let them 'play' with them. Many of the rays would push them around for awhile. It gave them something stimulating to due for awhile. The long term benefits of giving rays things that mentally challenge them have been proven as healthier and more active rays. Another way to change up their routine is put the food into a small hard plastic ball (like a gerbil or hamster ball) where they have to push it around to knock the food out.