Revealing mistake: At the dinner table when Lilith and Gretel are eating lunch with Lilith's "sons", Gretel takes a knife and stabs the boy closes to her in the hand. In the close up of the hand, it looks obviously rubber. That and there is already blood under it before the knife even hits.
Revealing mistake: The boy who escapes runs right past the Lilith son named John. John puts an arrow in this guy's back before Lilith calls him inside. As the boy gets back up to run, you can see a bulge under his shirt where the arrow is held. And as he moves, the arrow bobs and bounces around like it's super lose and not really in his back.