Usually, the son and moon represent something in the show. When the moon has blood in its mouth, it means someone is going to die or someone will die. The sun laughs creepily when a fight scene will be near or something twisted will come further in the episode. :) Hope this helps.
the moon grinds his teeth when someone in the world is dying and when blood is coming out of his mouth someone that night already died. I can't tell you what's up with the sun though cause i don't know