Freedom is a butterfly.

There's also this scene where they are chasing a butterfly. The butterfly is a metaphor for freedom. As long as they don't catch it, they will stay happy, but as soon as she catches it... The butterfly is just teasing them. The reality is looking for them all the time... If they catch the butterfly, the reality will catch them.
But still think the movie is happy. Men jag vet inte heller, när man gråter.