Creepy hidden Half-Life ambience sounds Part 1

More info: They&probably sounds from the canceled Valve previous game, Prospero and/or created to cause a heavy atmosphere. They were used a lot in Counter-Strike 1.6 Zombie Mod and latter in Left 4 Dead. Valve created similar sounds for Half-Life 2, never used in the final game but they appear in the leaked Beta, like the sound of a guitar played on reverse, weird voices and stuff. These sounds also appear in the sewers of Half-Life: Uplink and in a Xen factory, close to the end of the game. You can find them in the folder Half-Life/valve/sound/ambience/ with the names the_horror1.wav the_horror2.wav the_horror3.wav the_horror4.wav