Even a dead embryo will move as a result of the egg being tilted. In contrast, a live embryo moves in such a way that you can see specific movements, a foot moving, the chick making movement patterns instead of the whole body moving in response to the egg being tilted. If you are seeing definite movement patterns, give it the benefit of the doubt. However, I'd be giving it the sniff test every day, and ditch it if it starts to smell "dead."