I remember watching a movie called Fortress when we were kids. Starred Rachel Ward, Bryan Brown's missus.
Vicious masked crims take a class of young kids and their teacher hostage in the bush, they torment and chase them. At one point the teacher and the kids lose their shit and start hunting down the crims and killing them off.
The last scene a detective is telling the teacher how well they did to escape, but that they never found the heart of the boss crim, then the camera pans to a glass jar at the back of the classroom where the kids have saved it as a memento.
If I'm having a nightmare, those fuckers wearing masks are still half a chance to pop up at some stage...