Multiple personalities
Sam looked at the Mountain Master carefully.
He felt like something is wrong with him. His behavior in the battle right now is completely abnormal. After the first death, the mountain master acted like something serious had happened. He showed the classic signs of a self-absorbed individual who values his life way too much.
But there is this anger that he has whenever he was called a rodent. He is almost as angry as Sam when he was called a bastard.
He disregarded the consequence of the torturous feeling he gets when he dies.
Sam can even understand that. In fact, the usage of the term rodent is because Demon Soul swordsman told Sam that the Mountain Master will be pissed off because of this.
It is because in the past, the Mountain Master used to dig around the ground to set up traps to capture and kill his enemies. Just like how a rodent, particularly a rat or a bandicoot digs around in the ground and rocks.
That is part of his dirty laundry.