in a fight everyone is screaming all the time

In a fight everyone is screaming all the time and probably people will get scared before they get dead. 
Louis does fear damage and every blogger wants to be just like Louis when they grow up.  

we may never know...

Unless they have special training (fighter or soldier training doesn't count, but assassin or kill squad or being a tiger training does) living creatures who can feel fear and adrenaline scream every round that they can tell something intelligent is trying to kill or maim them.

Every round that they are screaming, they take 1 Fear Damage. Being gagged helps with the sound, but not with the fear. Other things like incredibly loud noises (such as bombs, or the screaming of armies or ghosts), seeing a friend die, or seeing an incredibly terrifying mask for the first time make them take 1 Fear Damage as well. If they're in a horrible place like a dungeon, fear damage is doubled. 

Fear Damage is dealt to HP like any other damage. Everyone gets 1.5x HP, 2x if they are a fighter.

At 1/2 HP, check morale (if you aren't doing normale Morale have people roll 1d12 over their current HP to succeed).
At 1/3 HP, you fall to your knees and cannot stand. You can crawl, and can continue to fight. 
At 0 HP, you fall to your belly and cannot rise. You can wriggle like a worm, and can continue to fight. 
When you fall below 0 HP, you are dead. If fear damage would kill you, you instead curl into a ball or pretend to be dead and wait for it to be all over. You finally stop screaming. 

 

we WILL never know...