it shows up even before you beat the game, just some foreshadowing most likely
Yeah, I've noticed that the dungeon seems to pulsate as if it is a living Organism and the deeper you go, the more red it turns.
At least that's what I think because the first level was black like rocks. When I went to level 2 and then. It started turning red and pulsating. I guess that would make sense why there's antibodies there. They're like white blood cells, seeing you as a virus. In which they have to exterminate.
But that doesn't explain the strings. It's almost like they're marionette puppets.