The contrast between a violent and blood-filled death and the presence of beautiful butterflies is a shocking image:

She spurted with her last strength and held ahead of them again. They were just behind her when she staggered into an open space where bright flowers grew and butterflies danced round each other and the air was hot and still.

Just a few moments later, the imagery of the butterflies comes into sharp focus again:

Jack found the throat and the hot blood spouted over his hands. The sow collapsed under them and they were heavy and fulfilled upon her. The butterflies still danced, preoccupied in the center of the clearing.

Butterflies are often symbolic of life and hope. In this scene of brutal death, readers are reminded of a couple of things. First, the boys' intrusion into a natural world has changed it and has introduced new threats to a world of innocent life. Additionally, as the mother pig staggers into a place of symbolic life, she also stumbles into the end of her own. However, her body will provide life for the boys (though their means of acquiring this sustenance are quite barbaric), and life will continue to go on through her death.

The butterflies also connote a sense of hope that remains in the midst of the brutality. Even in the midst of chaos, the flutter of hope lingers on.