That's so exciting! Healthier ones will move around when you move the cup or jostle it. They'll probably be flaring at the fish in the cup next to them. Look for one with vibrant colors. Keep in mind, just because they "look" healthy, doesn't mean they are. They can still have internal problems that you might not know until a couple months down the road. It's just a gamble you take, but we're here if you have any questions or concerns. :) Good luck and make sure to take lots of pictures!!