Is She Flirting or just being nice?

We, men, in most of our interactions with women (not necessarily when we approach a woman, but in every other situation), we consider every smile and every good behavior as their attraction to us and why not, a kind of flirting.

Recently a group of Norwegian psychologists wanted to do an experiment so they find what is true up to this issue and concluded that this incorrect -sexual- assessment, as they mentioned it, can be explained by human evolution.

See more in the following video.