Continuity mistake: When Hansel and Gretel are hiding from John, a jar of worms has been broken on the table they are under. Some worms fall through and land on Gretel's face, leaving dirt. The shot cuts to John, then right back to Gretel and suddenly her face has no dirt. Throughout that entire sequence, dirt and worms keep appearing and disappearing from her face and neck.
Picture added by Quantom X