Sustaining a temporary injury is quite common and usually results in nothing more than having to walk it off. I suggest when a man is severely injured however, putting him into the camp and allowing him time to heal. Orcs and Goblins love to knock the near dead. Also, make sure to have medicine on hand! If you do not, no healing will be done.
Making use of a Chapel's service will halve an injury's estimated healing time and prevents it from becoming infected.
With a single attack, there's an absolute minimum amount of 10 hitpoint damage required in order to inflict any injury, and then for any possible type of injury there's a relative amount required.
The exact amount varies with different injuries but it is generally between 25% and 50% of the victim's maximum hitpoints.
The more damage inflicted with a single attack, and the less maximum hitpoints the victim has, the more likely and more severe the injury will be. There is no random element to this
The perk "Crippling Strikes" lowers the threshold to inflict injuries by 33%, meaning that those 25% mentioned above would become ~16.5% and so on. The Perk is both more likely to inflict any injury at all, and more severe ones as well.
A vein on the throat has been cut, leading to massive hemorrhaging and ultimately death if no treated out of combat. If survived, it is followed by a period of severely lowered constitution due to loss of blood, and will leave a menacing scar.
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An artery has been cut, leading to massive hemorrhaging and ultimately death if not treated out of combat. If survived, it is followed by severely lowered constitution due to loss of blood.
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A close swing split this character's nose in two and made any attempt to breathe an exercise in swallowing copious amounts of blood.