Revealing mistake: When the three friends have a rest during their escape through the swamps you see water in the background where the ripples and the reflections are totally still, in contrast to all other shots before and after. It must be a painted backdrop. (01:05:20)
Revealing mistake: In the hut in the swamps Zack lights a candle. The resulting light is obviously from a spotlight because the flame and the shadows are perfectly still. (01:09:30)