If they have had their first sheds already it might just be bits of the old skin, as when they shed they do have a bit of skin that comes off their vent area but sometimes snags inside, that might be what you pushed out when trying to pop them.
I'm not sure what the blood is or what caused it but I just sexed some of my fresh hatchlings earlier this week and encountered the same thing from one of them, they seem to be fine otherwise though.
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