Why is it that we look at a total stranger for the first time, and get attracted or repulsed?

A glance does it.

Why do we happen to glance longer at some ?

What conversation do we have in that one glance that we just understand the other person, their history, their experience, their likes/ dislikes, their desires and sometimes even what could make them laugh or cry?

What exactly do we decode in that one look?

How does it work?
Is it that we perform a calculation too fast for even us to comprehend?
So while some people might not exactly be good looking, one look, and you know you would do well with them or be of help.
Certainly, we take a lot more than an individualÔÇÖs appearance; subtle details like dressing, manners, smile, even his/her reactions to the immediate environment are quickly evaluated.
But interestingly, such an evaluation is not possible for every individual we meet.
While some are scanned longer because they intrigue us, others are not even looked into the eye, because we could not intercept a certain ÔÇÿsomethingÔÇÖ about them.
What is that something that makes us act like magnets ÔÇô North pole drawn to South pole.

Are we as humans some pieces of a puzzle ?

Or are we, a design of such a high order that we just fit with some and not with others?
And if we are, will we ever be able to see through these designs?