I was sitting watching a movie and had a odd thought , I thought why is it in times of danger poeples instict is to scream I do not understand that ? I mean if your in an abandoned building in the forrest with no poeple but you and a killer and he is sneaking around looking for you or chasing you why do you scream ? if you are attacked and someone slashes at you why would you scream even if you know no one is thier but you and the danger ? I dont understand this fuction ? why do poeple scream so much ? why do poeple scream when thier in pain this too has no real fuction I understand crying but screaming I know this is odd I think to much .

Anyway I think screaming is a primitive reaction we have, most animals scream to scare\intimidate their enemy, or to cry for help.
Also psychologically it affects the one trying to kill you no matter how heartless he is, because it will make him know that you're not just an object.
By the way, your personality type is an INTJ (google it).
In terms of the pain thing, there have been studies that have shown that vocalisation helps you deal with the pain better. Swearing is even more effective.