The Delta Labs 4 level of the game consists of a few corridors red with messages written in blood such as "Die" or "Suffer". Go to the corner on the left side of the door leading to the teleporter room (where you fight two Hellknights) and punch the skeleton out of the way to reveal the message "You laugh, it works" written in blood letters on the wall behind it. You'll need to use your flashlight because that area is pitch black.