We do not know much about the fog.
It's a little strange how they are mostly human in almost everything, bar some traits.
Haruna has her obsession with words and their true meaning in a real life experience.
They all seem to lack the understanding behind human relations/feelings (well, I can't say I undertand that well...), but they still understand humor and know body language, do some, feel awkward or shame.
I wonder what is the message behind the show, I guess we might understand later when fog is better explained.