pleasure and pain

i was chilling watching tv with my friend. we were watching this movie, i think called the jackel or something and the woman was getting tortured. my friend's roomie was in the other room and says "OH WORD!" and my friend was like "what?" and the roomie said "i thought you were watching porn." for a moment i blinked and realized how right he was. who really knows the difference between moans of exstacy and moans of despair or pain? how different can the feelings be if the expression of them sound so similar? i guess they are both passionate feelings but why do we moan when we orgasm if that's what we use when we're in pain. a woman moans when she's getting good sex and moans nearly the same moan when she's giving birth. and why is it just for women? women's moans are all relatively the same unless she's a screamer but a man's moan can be different. he can range from plain moans, to grunts, to breathing, to "yeah", "what's my fucking name", to "oh.. ba-by" and you cant mistake any of those for pain. its interesting how thin the threshold between extremes really is.