There could be blood at the pip site if they hit a blood vessel. Don't bother the eggs while they're trying to hatch though, they've already gotten into position to do the hard work and if you disrupt them, it could make the journey that much more difficult b/c they have to re-position, diverting energy that is needed to do other work (like zipping).
It's hard not to get involved when you think things aren't going as they're "supposed to" but it's usually better to let Mother Nature do her thing, it usually works out the way it's supposed to.
Good luck and keep the camera handy!
While it's ideal not to move eggs, sometimes you do need to interfere in some way. I interfered with 2 of 8 babies in my recent hatch. One had gotten out of the eggshell, but it was still STRONGLY hinged. It popped shut around his little head and he could not figure out how to get out. I took pity on the poor little guy and opened the incubator and quickly took the eggshell off his (her?) little head.
The other was an egg that had been damaged at 9 days into the incubation (Quail have 16-17 days incubation so it was quite early.) I GLUED the egg over the damaged area -- we're talking a BIG area on a small coturnix egg. In fact, the damage was so extensive I put on three layers of glue. It ran down the egg and dried.
Where do you think that little one pipped? Right by the glue. 1/3 or more of it's zip line would have been through the glue. I gave it a few hours after I noticed the pip and decided I "would" intervene in that one. I gently made the pip hole larger, then zipped the eggshell for it about 1/4 or 1/3 of the way around the egg -- just the shell, though, not the membrane. The little thing started peeping LOUDLY when I started working, though it was silent before that. Once I popped it back in the incubator, it zipped the rest of the way and was completely out of the shell within 10-15 minutes. It was super strong and healthy. I really think it would have died in the shell, though, had I not helped. I did watch closely until he was out to make sure he didn't have other problems.
I should clarify -- I use a Brinsea mini advance. Humidity and temp recovery is super fast, plus I didn't have any other eggs that were pipped when I opened the incubator. I waited to interfere until that was the case.
There are definitely times to interfere. I'm not sure that your case is one of those, but if you think the chick will not make it, sometimes it's worth it. When there is blood, though, it generally isn't the right time to step in. This means the yolk is probably not absorbed yet.