The majority of scientists are agree that in the beginning of the Universe, so called Big Bang, Matter and Anti-Matter fight of the existence. As we all know regular Matter won, but with how much? They also agree that theoretically Anti-Matter exist today, but they don't know where... and since we're all made out of stardust, I think the evil trigger is that in some people is Anti-Matter present. They are like neutrinos...So small, that they can go right through solid ground and also you without collide with any particles. But when they do, they will annihilate each-other in a burst of energy.