Storybook opening: Bergens are miserable giants who believe they can only feel happy by eating trolls. Trolls live in a caged tree. Trollstice is a feast. Cute trolls, giant mouths, a yearly hunt. The film tells you the stakes before the songs get fun.
Theme. People-shaped prey is a different scare from a dragon. Sensitive kids may lock onto 'they eat the little ones' and carry it through every later joke.
What to say. You might say: 'The giants think eating trolls will make them happy. That is the scare of this film, and it is pretend. We can jump to the colourful village if the feast is too much.'
