Originally Posted by Metriakon

My kitty-cat came back. He ran away.

Fears can be acquired suddenly and cataclysmically when an extremely traumatic event polarizes a negative learning experience. This can be thought of as a variation on the post-traumatic shock theme. From the time of the negative experience onwards, the fear-inducing stimulus will be avoided or repulsed at all costs. Permanent learning of this type is facilitated by the release of a fight or flight neurotransmitter, called norephrenephrine.