Description[]
As a human, if your block bar drops to 0, you break your arm. While your arm is broken, your M1's (left mouse button) deal less damage, you also use your left hand for your sword instead of your right hand.
How to fix it[]
Bandages[]
You can fix it by going to any of the towns and buying a bandage, after a while it will disappear and your arm will be fixed.
Doctor[]
You can also visit the Doctor at Butterfly Estate to fix your broken arm immediately.