You know how Minecraft has a weird way of counting pixels?
Well, rumor has it Notch had a block added one Friday but removed it almost immediately...well, not NECESSARILY removed. He just mad eit inaccessible in the normal game. However, without this block in the game's code, getting to the "Nether" was impossible.
Now, the reason it was "removed" is because when players found out how to access it and place it, something weird happened.
It spawned a certain mob: a child.
Said child would follow the player around until they died. HOWEVER, if the CHILD were to die, they wouldn't necessarily disappear. The boy would remain there, screaming bloody murder. It screamed the most realistic of screams; many players vomited from the mere sound. This would continue no matter what part of the map the player went.
The body would remain there, slowly decaying after each minute until an hour passed and it became an unrecognizable mesh of flesh and blood...but the screaming still wouldn't stop.
The screaming could only be stopped if the player surrounded the body in a ring of Obsidion and set fire to the body. Upon doing so, the child would immediately jump and scream even louder. It would float up into the air, its eyes and mouth spouting flame.
It was then the body would slump to the ground, but the head would remain, still having the neural connections attached but floating there, still spouting flame. It would then grow until it was even more unrecognizeable from its former, decomposed self. It would grow paler and the eyes and mouth would close, but it would still scream.
Once the transformation is complete, you have a Ghast. The true origin of Ghasts is dead, torture children souls brought back through Satanic rituals. Notch removed this not because it revealed the truth, but because of what it did to players.
Every scream you hear in the Nether is a tortured child. Every time you killed a Ghast you hammered in even more pain into that poor child's miserable "life."
Ghasts only "attack" you because every time they open their mouths to scream to express their anguish to someone who may be able to help, fire shoots out.
(This story is credited to a person called Doctor Steel.)