It doesn't "swim" around. But will move as you move the egg. A blood ring denotes death, BUT if there is still veining and you're in doubt, I agree as long as it doesn't stink leave it in. Are you hand turning the eggs by chance? When you hand turn and you candle it looks totally different than when you are using a turner and it can appear to have a ring around the embryo. It's hard to explain. What ever side was facing up when you pick it up will have the development it will almost look like a circle or ring around it. As you turn the development will turn as well and come back to whatever side is facing up. Until the chick is formed it will look as though it's only developing on one side of the egg. You're best bet is to leave it in the incubator. If you have any that smell, those need to come out.
