One thing I don't quite understand about the film......*spoilers*

I'm guessing the person has to be awake during the ritual for it to work, but I just don't see why they couldn't of drugged the people so they're not in as much pain or as scared. I understood why they had to do what they did but I still felt so bad for those who went through all that not knowing why it had to be done....wouldn't it of been better to tie them down, put a drug in them to numb the pain...or maybe put them to sleep while using something to hold open their eyes.....maybe someone can explain it to me because at the end I sat there going "Oh okay I get why that had to happen....but what was the point of putting so much fear into them by chasing them and shooting them"