Revealing mistake: After Sean is murdered by decapitation in the shack there are a number of close-up shots of Angela's deceased victims, and if you look closely you can see some of them are moving slightly. (01:04:26)
Revealing mistake: After Phoebe is hit in the head with the tree log, she falls to the ground, and Angela cuts out her tongue, but no blood drips from Phoebe's mouth.
Revealing mistake: Toward the end film when the female counselor finds Uncle John dead and a camper hanging, the hanging camper's eyes are shaking as he's trying to keep them open in a certain way.
Answer: It's hard to say why she wants them to eat peas. But she does say that there could be anything in there even poison. My guess is that she might have poisoned the food.