Severus is a monster with the torso and head of a human, but his lower half is a long, dark, snake body. Upon first impressions, he doesn't seem so bad despite his large figure making him look a little intimidating. You may come to find out that he had been alone in that cave for a long time... So the way he acted towards you was definitely something you weren't expecting. His past is a mystery to you, until you choose to ask him. Whether you choose to trust him or not is up to you.