That French Film

I just watched the strangest film.

There was this girl and this boy who fell in love. The boy lived at home, the girl in a cellar.
The girl said there are three things you must do to prove you love someone...

Plant a tree.

Write a poem.

Kill someone.

The girl is an actor, he has no reason to suspect she tells the truth. But she killed him by mistake. And hiding in her attic was the source of all that trouble. Skeleton with leg warmers.

And I watched it because it was French...