The highly influential PT is one of PlayStation 4's best horror games -- it's a huge shame it was delisted when Konami cancelled Silent Hills. Despite being tiny in size, the playable teaser was big on atmosphere and jump scares, and it became an instant sensation when it was surprise released on PlayStation Store. One of the game's biggest triumphs was the unbelievable sense of dread and its ability to turn players completely paranoid. At times it would feel like something was following you, but there was nothing there when you turned around.
According to game hacker Lance McDonald, there actually is something following you, and it's doing so the entire time. The modder managed to hack into PT, and unlocked the game's camera from the player character. Doing so revealed an insane trick pulled off by the devs: Lisa is right behind you constantly.
You can read a little more in this Twitter thread. It includes a clip in which McDonald shows how Lisa attaches to you once you pick up the flashlight, creating those horrible shadows on the walls of the scariest corridor in games.
Very creepy stuff.