OK, so people in costumes are dressing in additional costumes over their regular costumes for Halloween. Notice that they're all dressed in opposites. Hamburgler, a known criminal, is dressed as a lawman. Ronald, ostensibly a friendly character meant to draw you in to eat, is dressed as a scarecrow, meant to scare birds away from eating. Grimace, known for his work with the Red Cross getting people to donate blood, is dressed as a vampire.
So what does this tell us about Birdy, dressed here as a life-saving nurse? Clearly she's secretly a serial killer.
I don't know what the deal is with the chicken McNuggets in costumes, that's just freaky.