The snake grows, but not its skin.
In order to stay alive, the snake has to leave behind its old skin.
Eva's character goes through this painful transformation.
From chrysalis to butterfly
Caterpillars slough into a chrysalis.
And turn into beautiful butterflies.
Iris's sloughing can be seen when she leaves the nest.
Sloughing means shedding off one's skin. It means starting a new life. Abandoning the old, the visible-- growing up.
It means “allowing for the perfect insect to appear” (Larousse).