Why is yawning contagious?

I've heard that if you yawn, somebody around you also begins to yawn and I've even found this to be true. So, if anybody knows why yawning is contagious, please let me know...

Is there really re-birth?

As any Indian would know, Karma is an inherent part of Hindu scriptures and texts but I would like to know how true is the concept of rebirth...How can such a claim be validated?

how important is "having expectations" from our friends and loved ones?

We often find that having expectations from our near and dear ones ,and not having them fulfilled, makes us angry, sad, dejected and hurt...So, how important is it that we should not have any expectations and just be contented with whatever we get..?As human beings, is it even possible?